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 $178.76   12.817%   $201.6717   $201.67   $201.65   $201.70  
  Purchase #2 $120.39   8.417%   $130.5232   $130.52   $130.50   $130.50  
  Purchase #3 $148.61   11.672%   $165.9558   $165.96   $165.95   $166.00  
  Purchase #4 $60.54   7.311%   $64.9661   $64.97   $64.95   $65.00  
  Purchase #5 $149.31   11.283%   $166.1566   $166.16   $166.15   $166.20  
  Purchase #6 $161.65   4.517%   $168.9517   $168.95   $168.95   $169.00  
  Purchase #7 $59.59   12.583%   $67.0882   $67.09   $67.10   $67.10  
  7 purchase totals = $878.85       $965.3133   $965.32   $965.25   $965.50