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 $33.83   7.293%   $36.2972   $36.30   $36.30   $36.30  
  Purchase #2 $149.66   5.792%   $158.3283   $158.33   $158.35   $158.30  
  Purchase #3 $67.80   13.452%   $76.9205   $76.92   $76.90   $76.90  
  Purchase #4 $51.39   5.384%   $54.1568   $54.16   $54.15   $54.20  
  Purchase #5 $85.70   9.472%   $93.8175   $93.82   $93.80   $93.80  
  Purchase #6 $190.72   5.747%   $201.6807   $201.68   $201.70   $201.70  
  Purchase #7 $33.44   5.246%   $35.1943   $35.19   $35.20   $35.20  
  7 purchase totals = $612.54       $656.3953   $656.40   $656.40   $656.40