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 $132.63   6.872%   $141.7443   $141.74   $141.75   $141.70  
  Purchase #2 $20.35   11.436%   $22.6772   $22.68   $22.70   $22.70  
  Purchase #3 $86.40   5.576%   $91.2177   $91.22   $91.20   $91.20  
  Purchase #4 $125.97   11.403%   $140.3344   $140.33   $140.35   $140.30  
  Purchase #5 $212.34   9.267%   $232.0175   $232.02   $232.00   $232.00  
  Purchase #6 $229.33   4.614%   $239.9113   $239.91   $239.90   $239.90  
  Purchase #7 $138.39   11.223%   $153.9215   $153.92   $153.90   $153.90  
  7 purchase totals = $945.41       $1,021.8239   $1,021.82   $1,021.80   $1,021.70