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 $235.45   4.704%   $246.5256   $246.53   $246.55   $246.50  
  Purchase #2 $187.59   5.413%   $197.7442   $197.74   $197.75   $197.70  
  Purchase #3 $103.83   4.254%   $108.2469   $108.25   $108.25   $108.20  
  Purchase #4 $160.99   10.831%   $178.4268   $178.43   $178.45   $178.40  
  Purchase #5 $117.76   5.186%   $123.867   $123.87   $123.85   $123.90  
  Purchase #6 $16.59   4.364%   $17.314   $17.31   $17.30   $17.30  
  Purchase #7 $134.95   10.389%   $148.97   $148.97   $148.95   $149.00  
  7 purchase totals = $957.16       $1,021.0945   $1,021.10   $1,021.10   $1,021.00