Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.66   6.462%   $261.5345   $261.53   $261.55   $261.50  
  Purchase #2 $197.97   10.283%   $218.3273   $218.33   $218.35   $218.30  
  Purchase #3 $175.91   10.194%   $193.8423   $193.84   $193.85   $193.80  
  Purchase #4 $245.44   4.729%   $257.0469   $257.05   $257.05   $257.00  
  Purchase #5 $125.65   6.361%   $133.6426   $133.64   $133.65   $133.60  
  Purchase #6 $110.99   13.836%   $126.3466   $126.35   $126.35   $126.30  
  Purchase #7 $172.86   12.220%   $193.9835   $193.98   $194.00   $194.00  
  7 purchase totals = $1,274.48       $1,384.7237   $1,384.72   $1,384.80   $1,384.50