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 $222.89   12.617%   $251.012   $251.01   $251.00   $251.00  
  Purchase #2 $60.57   10.620%   $67.0025   $67.00   $67.00   $67.00  
  Purchase #3 $242.38   13.567%   $275.2637   $275.26   $275.25   $275.30  
  Purchase #4 $14.85   12.297%   $16.6761   $16.68   $16.70   $16.70  
  Purchase #5 $69.62   9.521%   $76.2485   $76.25   $76.25   $76.20  
  Purchase #6 $21.36   3.519%   $22.1117   $22.11   $22.10   $22.10  
  Purchase #7 $219.80   4.363%   $229.3899   $229.39   $229.40   $229.40  
  7 purchase totals = $851.47       $937.7044   $937.70   $937.70   $937.70