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 $202.30   8.562%   $219.6209   $219.62   $219.60   $219.60  
  Purchase #2 $7.66   3.643%   $7.9391   $7.94   $7.95   $7.90  
  Purchase #3 $216.25   13.683%   $245.8395   $245.84   $245.85   $245.80  
  Purchase #4 $59.52   6.579%   $63.4358   $63.44   $63.45   $63.40  
  Purchase #5 $169.67   9.588%   $185.938   $185.94   $185.95   $185.90  
  Purchase #6 $126.26   5.862%   $133.6614   $133.66   $133.65   $133.70  
  Purchase #7 $44.26   5.105%   $46.5195   $46.52   $46.50   $46.50  
  7 purchase totals = $825.92       $902.9542   $902.96   $902.95   $902.80