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 $241.26   13.276%   $273.2897   $273.29   $273.30   $273.30  
  Purchase #2 $87.75   7.104%   $93.9838   $93.98   $94.00   $94.00  
  Purchase #3 $236.28   7.697%   $254.4665   $254.47   $254.45   $254.50  
  Purchase #4 $244.25   10.279%   $269.3565   $269.36   $269.35   $269.40  
  Purchase #5 $25.95   9.210%   $28.34   $28.34   $28.35   $28.30  
  Purchase #6 $86.71   6.105%   $92.0036   $92.00   $92.00   $92.00  
  Purchase #7 $177.90   5.468%   $187.6276   $187.63   $187.65   $187.60  
  7 purchase totals = $1,100.10       $1,199.0677   $1,199.07   $1,199.10   $1,199.10