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 $57.38   13.262%   $64.9897   $64.99   $65.00   $65.00  
  Purchase #2 $84.62   13.352%   $95.9185   $95.92   $95.90   $95.90  
  Purchase #3 $52.57   5.221%   $55.3147   $55.31   $55.30   $55.30  
  Purchase #4 $94.99   10.415%   $104.8832   $104.88   $104.90   $104.90  
  Purchase #5 $43.93   7.573%   $47.2568   $47.26   $47.25   $47.30  
  Purchase #6 $22.43   13.823%   $25.5305   $25.53   $25.55   $25.50  
  Purchase #7 $61.62   7.816%   $66.4362   $66.44   $66.45   $66.40  
  7 purchase totals = $417.54       $460.3296   $460.33   $460.35   $460.30