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 $83.29   13.637%   $94.6483   $94.65   $94.65   $94.60  
  Purchase #2 $171.32   6.756%   $182.8944   $182.89   $182.90   $182.90  
  Purchase #3 $219.76   12.697%   $247.6629   $247.66   $247.65   $247.70  
  Purchase #4 $96.93   4.800%   $101.5826   $101.58   $101.60   $101.60  
  Purchase #5 $138.89   8.867%   $151.2054   $151.21   $151.20   $151.20  
  Purchase #6 $72.29   4.210%   $75.3334   $75.33   $75.35   $75.30  
  Purchase #7 $38.28   5.199%   $40.2702   $40.27   $40.25   $40.30  
  7 purchase totals = $820.76       $893.5972   $893.59   $893.60   $893.60