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 $70.46   7.378%   $75.6585   $75.66   $75.65   $75.70  
  Purchase #2 $224.68   9.485%   $245.9909   $245.99   $246.00   $246.00  
  Purchase #3 $76.84   6.317%   $81.694   $81.69   $81.70   $81.70  
  Purchase #4 $49.37   11.724%   $55.1581   $55.16   $55.15   $55.20  
  Purchase #5 $32.71   3.756%   $33.9386   $33.94   $33.95   $33.90  
  Purchase #6 $210.74   5.817%   $222.9987   $223.00   $223.00   $223.00  
  Purchase #7 $168.31   6.312%   $178.9337   $178.93   $178.95   $178.90  
  7 purchase totals = $833.11       $894.3725   $894.37   $894.40   $894.40