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 $60.78   6.613%   $64.7994   $64.80   $64.80   $64.80  
  Purchase #2 $164.98   7.754%   $177.7725   $177.77   $177.75   $177.80  
  Purchase #3 $147.33   7.187%   $157.9186   $157.92   $157.90   $157.90  
  Purchase #4 $161.41   13.302%   $182.8808   $182.88   $182.90   $182.90  
  Purchase #5 $193.67   11.869%   $216.6567   $216.66   $216.65   $216.70  
  Purchase #6 $197.52   8.840%   $214.9808   $214.98   $215.00   $215.00  
  Purchase #7 $180.81   4.735%   $189.3714   $189.37   $189.35   $189.40  
  7 purchase totals = $1,106.50       $1,204.3802   $1,204.38   $1,204.35   $1,204.50