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 $52.59   9.487%   $57.5792   $57.58   $57.60   $57.60  
  Purchase #2 $98.70   9.439%   $108.0163   $108.02   $108.00   $108.00  
  Purchase #3 $229.94   7.603%   $247.4223   $247.42   $247.40   $247.40  
  Purchase #4 $209.66   12.273%   $235.3916   $235.39   $235.40   $235.40  
  Purchase #5 $68.27   5.838%   $72.2556   $72.26   $72.25   $72.30  
  Purchase #6 $36.50   9.292%   $39.8916   $39.89   $39.90   $39.90  
  Purchase #7 $164.33   11.787%   $183.6996   $183.70   $183.70   $183.70  
  7 purchase totals = $859.99       $944.2562   $944.26   $944.25   $944.30