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 $182.69   13.266%   $206.9257   $206.93   $206.95   $206.90  
  Purchase #2 $72.65   5.629%   $76.7395   $76.74   $76.75   $76.70  
  Purchase #3 $89.35   4.827%   $93.6629   $93.66   $93.65   $93.70  
  Purchase #4 $223.60   9.175%   $244.1153   $244.12   $244.10   $244.10  
  Purchase #5 $57.53   7.841%   $62.0409   $62.04   $62.05   $62.00  
  Purchase #6 $49.93   8.639%   $54.2435   $54.24   $54.25   $54.20  
  Purchase #7 $30.85   7.856%   $33.2736   $33.27   $33.25   $33.30  
  7 purchase totals = $706.60       $771.0014   $771.00   $771.00   $770.90