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 $236.47   12.498%   $266.024   $266.02   $266.00   $266.00  
  Purchase #2 $62.80   11.702%   $70.1489   $70.15   $70.15   $70.10  
  Purchase #3 $17.79   11.206%   $19.7835   $19.78   $19.80   $19.80  
  Purchase #4 $130.32   13.824%   $148.3354   $148.34   $148.35   $148.30  
  Purchase #5 $132.78   11.334%   $147.8293   $147.83   $147.85   $147.80  
  Purchase #6 $238.87   3.375%   $246.9319   $246.93   $246.95   $246.90  
  Purchase #7 $158.51   10.472%   $175.1092   $175.11   $175.10   $175.10  
  7 purchase totals = $977.54       $1,074.1622   $1,074.16   $1,074.20   $1,074.00