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 $10.84   7.462%   $11.6489   $11.65   $11.65   $11.60  
  Purchase #2 $236.88   10.563%   $261.9016   $261.90   $261.90   $261.90  
  Purchase #3 $175.28   10.145%   $193.0622   $193.06   $193.05   $193.10  
  Purchase #4 $91.66   13.460%   $103.9974   $104.00   $104.00   $104.00  
  Purchase #5 $118.99   11.178%   $132.2907   $132.29   $132.30   $132.30  
  Purchase #6 $110.84   10.848%   $122.8639   $122.86   $122.85   $122.90  
  Purchase #7 $75.85   12.795%   $85.555   $85.56   $85.55   $85.60  
  7 purchase totals = $820.34       $911.3197   $911.32   $911.30   $911.40