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 $214.85   10.763%   $237.9743   $237.97   $237.95   $238.00  
  Purchase #2 $88.82   11.410%   $98.9544   $98.95   $98.95   $99.00  
  Purchase #3 $119.84   10.503%   $132.4268   $132.43   $132.45   $132.40  
  Purchase #4 $110.59   13.686%   $125.7253   $125.73   $125.75   $125.70  
  Purchase #5 $53.65   6.608%   $57.1952   $57.20   $57.20   $57.20  
  Purchase #6 $122.55   7.465%   $131.6984   $131.70   $131.70   $131.70  
  Purchase #7 $8.75   9.824%   $9.6096   $9.61   $9.60   $9.60  
  7 purchase totals = $719.05       $793.5840   $793.59   $793.60   $793.60