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 $58.52   4.643%   $61.2371   $61.24   $61.25   $61.20  
  Purchase #2 $242.56   5.297%   $255.4084   $255.41   $255.40   $255.40  
  Purchase #3 $106.90   12.780%   $120.5618   $120.56   $120.55   $120.60  
  Purchase #4 $94.58   13.472%   $107.3218   $107.32   $107.30   $107.30  
  Purchase #5 $67.46   4.680%   $70.6171   $70.62   $70.60   $70.60  
  Purchase #6 $65.92   3.284%   $68.0848   $68.08   $68.10   $68.10  
  Purchase #7 $107.82   9.399%   $117.954   $117.95   $117.95   $118.00  
  7 purchase totals = $743.76       $801.1850   $801.18   $801.15   $801.20