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 $56.71   6.244%   $60.251   $60.25   $60.25   $60.30  
  Purchase #2 $173.31   3.154%   $178.7762   $178.78   $178.80   $178.80  
  Purchase #3 $204.42   6.532%   $217.7727   $217.77   $217.75   $217.80  
  Purchase #4 $33.96   5.211%   $35.7297   $35.73   $35.75   $35.70  
  Purchase #5 $249.81   7.217%   $267.8388   $267.84   $267.85   $267.80  
  Purchase #6 $124.61   4.512%   $130.2324   $130.23   $130.25   $130.20  
  Purchase #7 $163.36   7.730%   $175.9877   $175.99   $176.00   $176.00  
  7 purchase totals = $1,006.18       $1,066.5885   $1,066.59   $1,066.65   $1,066.60