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 $222.63   9.654%   $244.1227   $244.12   $244.10   $244.10  
  Purchase #2 $85.63   10.592%   $94.6999   $94.70   $94.70   $94.70  
  Purchase #3 $230.54   6.855%   $246.3435   $246.34   $246.35   $246.30  
  Purchase #4 $77.44   8.375%   $83.9256   $83.93   $83.95   $83.90  
  Purchase #5 $58.94   4.783%   $61.7591   $61.76   $61.75   $61.80  
  Purchase #6 $194.94   3.533%   $201.8272   $201.83   $201.85   $201.80  
  Purchase #7 $62.83   11.143%   $69.8311   $69.83   $69.85   $69.80  
  7 purchase totals = $932.95       $1,002.5091   $1,002.51   $1,002.55   $1,002.40