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 $60.58   3.384%   $62.63   $62.63   $62.65   $62.60  
  Purchase #2 $237.34   11.447%   $264.5083   $264.51   $264.50   $264.50  
  Purchase #3 $47.56   6.511%   $50.6566   $50.66   $50.65   $50.70  
  Purchase #4 $81.26   3.483%   $84.0903   $84.09   $84.10   $84.10  
  Purchase #5 $166.80   8.214%   $180.501   $180.50   $180.50   $180.50  
  Purchase #6 $35.73   5.731%   $37.7777   $37.78   $37.80   $37.80  
  Purchase #7 $147.26   6.135%   $156.2944   $156.29   $156.30   $156.30  
  7 purchase totals = $776.53       $836.4583   $836.46   $836.50   $836.50