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 $51.78   13.614%   $58.8293   $58.83   $58.85   $58.80  
  Purchase #2 $232.57   5.504%   $245.3707   $245.37   $245.35   $245.40  
  Purchase #3 $145.82   5.572%   $153.9451   $153.95   $153.95   $153.90  
  Purchase #4 $107.69   12.554%   $121.2094   $121.21   $121.20   $121.20  
  Purchase #5 $42.90   11.681%   $47.9111   $47.91   $47.90   $47.90  
  Purchase #6 $166.66   3.727%   $172.8714   $172.87   $172.85   $172.90  
  Purchase #7 $140.44   12.787%   $158.3981   $158.40   $158.40   $158.40  
  7 purchase totals = $887.86       $958.5351   $958.54   $958.50   $958.50