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 $206.29   9.223%   $225.3161   $225.32   $225.30   $225.30  
  Purchase #2 $45.93   7.319%   $49.2916   $49.29   $49.30   $49.30  
  Purchase #3 $180.67   8.175%   $195.4398   $195.44   $195.45   $195.40  
  Purchase #4 $249.46   8.269%   $270.0878   $270.09   $270.10   $270.10  
  Purchase #5 $148.88   13.394%   $168.821   $168.82   $168.80   $168.80  
  Purchase #6 $241.88   13.483%   $274.4927   $274.49   $274.50   $274.50  
  Purchase #7 $245.45   12.533%   $276.2122   $276.21   $276.20   $276.20  
  7 purchase totals = $1,318.56       $1,459.6612   $1,459.66   $1,459.65   $1,459.60