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 $242.49   8.822%   $263.8825   $263.88   $263.90   $263.90  
  Purchase #2 $11.41   8.310%   $12.3582   $12.36   $12.35   $12.40  
  Purchase #3 $249.67   9.596%   $273.6283   $273.63   $273.65   $273.60  
  Purchase #4 $187.56   3.857%   $194.7942   $194.79   $194.80   $194.80  
  Purchase #5 $47.32   8.232%   $51.2154   $51.22   $51.20   $51.20  
  Purchase #6 $217.84   12.286%   $244.6038   $244.60   $244.60   $244.60  
  Purchase #7 $194.75   9.579%   $213.4051   $213.41   $213.40   $213.40  
  7 purchase totals = $1,151.04       $1,253.8875   $1,253.89   $1,253.90   $1,253.90