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 $194.46   7.206%   $208.4728   $208.47   $208.45   $208.50  
  Purchase #2 $32.57   6.761%   $34.7721   $34.77   $34.75   $34.80  
  Purchase #3 $176.86   10.261%   $195.0076   $195.01   $195.00   $195.00  
  Purchase #4 $44.65   5.872%   $47.2718   $47.27   $47.25   $47.30  
  Purchase #5 $38.30   13.624%   $43.518   $43.52   $43.50   $43.50  
  Purchase #6 $190.50   11.831%   $213.0381   $213.04   $213.05   $213.00  
  Purchase #7 $118.77   5.558%   $125.3712   $125.37   $125.35   $125.40  
  7 purchase totals = $796.11       $867.4516   $867.45   $867.35   $867.50