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 $85.34   9.695%   $93.6137   $93.61   $93.60   $93.60  
  Purchase #2 $11.62   13.717%   $13.2139   $13.21   $13.20   $13.20  
  Purchase #3 $244.37   10.468%   $269.9507   $269.95   $269.95   $270.00  
  Purchase #4 $200.80   12.828%   $226.5586   $226.56   $226.55   $226.60  
  Purchase #5 $195.92   12.144%   $219.7125   $219.71   $219.70   $219.70  
  Purchase #6 $86.68   9.286%   $94.7291   $94.73   $94.75   $94.70  
  Purchase #7 $120.37   4.428%   $125.7   $125.70   $125.70   $125.70  
  7 purchase totals = $945.10       $1,043.4785   $1,043.47   $1,043.45   $1,043.50