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 $56.59   4.165%   $58.947   $58.95   $58.95   $58.90  
  Purchase #2 $88.40   8.333%   $95.7664   $95.77   $95.75   $95.80  
  Purchase #3 $117.84   5.217%   $123.9877   $123.99   $124.00   $124.00  
  Purchase #4 $68.49   13.581%   $77.7916   $77.79   $77.80   $77.80  
  Purchase #5 $133.36   9.629%   $146.2012   $146.20   $146.20   $146.20  
  Purchase #6 $188.84   12.641%   $212.7113   $212.71   $212.70   $212.70  
  Purchase #7 $129.51   4.748%   $135.6591   $135.66   $135.65   $135.70  
  7 purchase totals = $783.03       $851.0643   $851.07   $851.05   $851.10