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 $104.41   9.618%   $114.4522   $114.45   $114.45   $114.50  
  Purchase #2 $122.62   10.631%   $135.6557   $135.66   $135.65   $135.70  
  Purchase #3 $178.31   4.800%   $186.8689   $186.87   $186.85   $186.90  
  Purchase #4 $88.27   9.141%   $96.3388   $96.34   $96.35   $96.30  
  Purchase #5 $154.73   12.648%   $174.3003   $174.30   $174.30   $174.30  
  Purchase #6 $61.53   5.389%   $64.8459   $64.85   $64.85   $64.80  
  Purchase #7 $59.32   9.490%   $64.9495   $64.95   $64.95   $64.90  
  7 purchase totals = $769.19       $837.4113   $837.42   $837.40   $837.40