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 $179.36   13.820%   $204.1476   $204.15   $204.15   $204.10  
  Purchase #2 $194.68   7.148%   $208.5957   $208.60   $208.60   $208.60  
  Purchase #3 $76.81   7.259%   $82.3856   $82.39   $82.40   $82.40  
  Purchase #4 $168.54   10.152%   $185.6502   $185.65   $185.65   $185.70  
  Purchase #5 $133.25   4.803%   $139.65   $139.65   $139.65   $139.70  
  Purchase #6 $117.35   5.816%   $124.1751   $124.18   $124.20   $124.20  
  Purchase #7 $20.72   7.809%   $22.338   $22.34   $22.35   $22.30  
  7 purchase totals = $890.71       $966.9422   $966.96   $967.00   $967.00