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 $234.45   13.673%   $266.5063   $266.51   $266.50   $266.50  
  Purchase #2 $155.81   11.589%   $173.8668   $173.87   $173.85   $173.90  
  Purchase #3 $219.63   11.691%   $245.3069   $245.31   $245.30   $245.30  
  Purchase #4 $130.39   8.616%   $141.6244   $141.62   $141.60   $141.60  
  Purchase #5 $158.42   7.399%   $170.1415   $170.14   $170.15   $170.10  
  Purchase #6 $199.74   6.579%   $212.8809   $212.88   $212.90   $212.90  
  Purchase #7 $47.27   9.215%   $51.6259   $51.63   $51.65   $51.60  
  7 purchase totals = $1,145.71       $1,261.9527   $1,261.96   $1,261.95   $1,261.90