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 $58.97   11.259%   $65.6094   $65.61   $65.60   $65.60  
  Purchase #2 $181.42   6.559%   $193.3193   $193.32   $193.30   $193.30  
  Purchase #3 $47.83   6.368%   $50.8758   $50.88   $50.90   $50.90  
  Purchase #4 $46.56   5.162%   $48.9634   $48.96   $48.95   $49.00  
  Purchase #5 $95.96   6.348%   $102.0515   $102.05   $102.05   $102.10  
  Purchase #6 $79.65   8.683%   $86.566   $86.57   $86.55   $86.60  
  Purchase #7 $210.56   6.677%   $224.6191   $224.62   $224.60   $224.60  
  7 purchase totals = $720.95       $772.0045   $772.01   $771.95   $772.10