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 $231.37   6.167%   $245.6386   $245.64   $245.65   $245.60  
  Purchase #2 $179.56   4.499%   $187.6384   $187.64   $187.65   $187.60  
  Purchase #3 $61.58   10.692%   $68.1641   $68.16   $68.15   $68.20  
  Purchase #4 $25.57   11.220%   $28.439   $28.44   $28.45   $28.40  
  Purchase #5 $119.95   10.512%   $132.5591   $132.56   $132.55   $132.60  
  Purchase #6 $78.90   10.395%   $87.1017   $87.10   $87.10   $87.10  
  Purchase #7 $247.64   5.534%   $261.3444   $261.34   $261.35   $261.30  
  7 purchase totals = $944.57       $1,010.8853   $1,010.88   $1,010.90   $1,010.80