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 $169.67   7.682%   $182.704   $182.70   $182.70   $182.70  
  Purchase #2 $78.55   6.668%   $83.7877   $83.79   $83.80   $83.80  
  Purchase #3 $144.78   11.737%   $161.7728   $161.77   $161.75   $161.80  
  Purchase #4 $220.35   5.440%   $232.337   $232.34   $232.35   $232.30  
  Purchase #5 $10.90   13.676%   $12.3907   $12.39   $12.40   $12.40  
  Purchase #6 $161.59   8.654%   $175.574   $175.57   $175.55   $175.60  
  Purchase #7 $100.28   7.688%   $107.9895   $107.99   $108.00   $108.00  
  7 purchase totals = $886.12       $956.5557   $956.55   $956.55   $956.60