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 $101.82   12.195%   $114.2369   $114.24   $114.25   $114.20  
  Purchase #2 $55.97   4.837%   $58.6773   $58.68   $58.70   $58.70  
  Purchase #3 $141.37   7.392%   $151.8201   $151.82   $151.80   $151.80  
  Purchase #4 $100.55   13.157%   $113.7794   $113.78   $113.80   $113.80  
  Purchase #5 $188.44   9.540%   $206.4172   $206.42   $206.40   $206.40  
  Purchase #6 $65.64   4.596%   $68.6568   $68.66   $68.65   $68.70  
  Purchase #7 $131.34   13.411%   $148.954   $148.95   $148.95   $149.00  
  7 purchase totals = $785.13       $862.5417   $862.55   $862.55   $862.60