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 $188.65   3.851%   $195.9149   $195.91   $195.90   $195.90  
  Purchase #2 $236.95   11.679%   $264.6234   $264.62   $264.60   $264.60  
  Purchase #3 $101.46   13.381%   $115.0364   $115.04   $115.05   $115.00  
  Purchase #4 $148.71   4.715%   $155.7217   $155.72   $155.70   $155.70  
  Purchase #5 $200.37   3.524%   $207.431   $207.43   $207.45   $207.40  
  Purchase #6 $232.50   7.283%   $249.433   $249.43   $249.45   $249.40  
  Purchase #7 $157.77   3.735%   $163.6627   $163.66   $163.65   $163.70  
  7 purchase totals = $1,266.41       $1,351.8231   $1,351.81   $1,351.80   $1,351.70