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 $158.33   8.113%   $171.1753   $171.18   $171.20   $171.20  
  Purchase #2 $85.99   12.166%   $96.4515   $96.45   $96.45   $96.50  
  Purchase #3 $91.30   11.152%   $101.4818   $101.48   $101.50   $101.50  
  Purchase #4 $67.34   10.421%   $74.3575   $74.36   $74.35   $74.40  
  Purchase #5 $13.60   4.741%   $14.2448   $14.24   $14.25   $14.20  
  Purchase #6 $180.63   10.783%   $200.1073   $200.11   $200.10   $200.10  
  Purchase #7 $208.52   4.337%   $217.5635   $217.56   $217.55   $217.60  
  7 purchase totals = $805.71       $875.3817   $875.38   $875.40   $875.50