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 $164.55   6.104%   $174.5941   $174.59   $174.60   $174.60  
  Purchase #2 $126.31   8.302%   $136.7963   $136.80   $136.80   $136.80  
  Purchase #3 $150.95   12.330%   $169.5621   $169.56   $169.55   $169.60  
  Purchase #4 $55.93   3.462%   $57.8663   $57.87   $57.85   $57.90  
  Purchase #5 $22.65   7.661%   $24.3852   $24.39   $24.40   $24.40  
  Purchase #6 $104.90   7.284%   $112.5409   $112.54   $112.55   $112.50  
  Purchase #7 $242.31   13.153%   $274.181   $274.18   $274.20   $274.20  
  7 purchase totals = $867.60       $949.9259   $949.93   $949.95   $950.00