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 $66.37   13.161%   $75.105   $75.11   $75.10   $75.10  
  Purchase #2 $87.98   8.157%   $95.1565   $95.16   $95.15   $95.20  
  Purchase #3 $164.59   5.865%   $174.2432   $174.24   $174.25   $174.20  
  Purchase #4 $186.70   8.639%   $202.829   $202.83   $202.85   $202.80  
  Purchase #5 $56.43   6.496%   $60.0957   $60.10   $60.10   $60.10  
  Purchase #6 $81.45   6.488%   $86.7345   $86.73   $86.75   $86.70  
  Purchase #7 $81.63   6.840%   $87.2135   $87.21   $87.20   $87.20  
  7 purchase totals = $725.15       $781.3774   $781.38   $781.40   $781.30