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 $204.37   7.447%   $219.5894   $219.59   $219.60   $219.60  
  Purchase #2 $89.83   6.266%   $95.4587   $95.46   $95.45   $95.50  
  Purchase #3 $32.81   11.616%   $36.6212   $36.62   $36.60   $36.60  
  Purchase #4 $244.93   13.683%   $278.4438   $278.44   $278.45   $278.40  
  Purchase #5 $132.68   13.770%   $150.95   $150.95   $150.95   $151.00  
  Purchase #6 $170.53   4.484%   $178.1766   $178.18   $178.20   $178.20  
  Purchase #7 $231.51   13.398%   $262.5277   $262.53   $262.55   $262.50  
  7 purchase totals = $1,106.66       $1,221.7674   $1,221.77   $1,221.80   $1,221.80