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 $47.39   10.781%   $52.4991   $52.50   $52.50   $52.50  
  Purchase #2 $199.71   11.531%   $222.7386   $222.74   $222.75   $222.70  
  Purchase #3 $216.89   13.626%   $246.4434   $246.44   $246.45   $246.40  
  Purchase #4 $174.85   4.375%   $182.4997   $182.50   $182.50   $182.50  
  Purchase #5 $10.93   9.243%   $11.9403   $11.94   $11.95   $11.90  
  Purchase #6 $32.45   7.759%   $34.9678   $34.97   $34.95   $35.00  
  Purchase #7 $243.91   6.697%   $260.2447   $260.24   $260.25   $260.20  
  7 purchase totals = $926.13       $1,011.3336   $1,011.33   $1,011.35   $1,011.20