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 $84.31   9.689%   $92.4788   $92.48   $92.50   $92.50  
  Purchase #2 $41.50   12.339%   $46.6207   $46.62   $46.60   $46.60  
  Purchase #3 $231.92   6.354%   $246.6562   $246.66   $246.65   $246.70  
  Purchase #4 $48.64   5.487%   $51.3089   $51.31   $51.30   $51.30  
  Purchase #5 $58.51   10.500%   $64.6536   $64.65   $64.65   $64.70  
  Purchase #6 $249.27   9.703%   $273.4567   $273.46   $273.45   $273.50  
  Purchase #7 $221.73   7.786%   $238.9939   $238.99   $239.00   $239.00  
  7 purchase totals = $935.88       $1,014.1688   $1,014.17   $1,014.15   $1,014.30