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 $91.84   6.255%   $97.5846   $97.58   $97.60   $97.60  
  Purchase #2 $250.77   5.538%   $264.6576   $264.66   $264.65   $264.70  
  Purchase #3 $8.67   10.466%   $9.5774   $9.58   $9.60   $9.60  
  Purchase #4 $221.79   3.180%   $228.8429   $228.84   $228.85   $228.80  
  Purchase #5 $236.71   5.448%   $249.606   $249.61   $249.60   $249.60  
  Purchase #6 $95.25   8.872%   $103.7006   $103.70   $103.70   $103.70  
  Purchase #7 $217.70   8.844%   $236.9534   $236.95   $236.95   $237.00  
  7 purchase totals = $1,122.73       $1,190.9225   $1,190.92   $1,190.95   $1,191.00