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 $223.53   11.230%   $248.6324   $248.63   $248.65   $248.60  
  Purchase #2 $250.72   10.262%   $276.4489   $276.45   $276.45   $276.40  
  Purchase #3 $196.66   12.125%   $220.505   $220.51   $220.50   $220.50  
  Purchase #4 $195.89   11.720%   $218.8483   $218.85   $218.85   $218.80  
  Purchase #5 $190.66   5.865%   $201.8422   $201.84   $201.85   $201.80  
  Purchase #6 $176.48   12.661%   $198.8241   $198.82   $198.80   $198.80  
  Purchase #7 $41.34   10.172%   $45.5451   $45.55   $45.55   $45.50  
  7 purchase totals = $1,275.28       $1,410.6460   $1,410.65   $1,410.65   $1,410.40