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 $86.28   11.469%   $96.1755   $96.18   $96.20   $96.20  
  Purchase #2 $187.67   7.633%   $201.9949   $201.99   $202.00   $202.00  
  Purchase #3 $154.41   6.440%   $164.354   $164.35   $164.35   $164.40  
  Purchase #4 $163.25   6.238%   $173.4335   $173.43   $173.45   $173.40  
  Purchase #5 $136.95   13.797%   $155.845   $155.85   $155.85   $155.80  
  Purchase #6 $31.32   11.776%   $35.0082   $35.01   $35.00   $35.00  
  Purchase #7 $146.55   5.579%   $154.726   $154.73   $154.75   $154.70  
  7 purchase totals = $906.43       $981.5371   $981.54   $981.60   $981.50