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 $65.75   11.804%   $73.5111   $73.51   $73.50   $73.50  
  Purchase #2 $79.70   6.211%   $84.6502   $84.65   $84.65   $84.70  
  Purchase #3 $68.81   4.519%   $71.9195   $71.92   $71.90   $71.90  
  Purchase #4 $231.71   6.206%   $246.0899   $246.09   $246.10   $246.10  
  Purchase #5 $166.43   11.867%   $186.1802   $186.18   $186.20   $186.20  
  Purchase #6 $44.26   7.343%   $47.51   $47.51   $47.50   $47.50  
  Purchase #7 $168.48   3.501%   $174.3785   $174.38   $174.40   $174.40  
  7 purchase totals = $825.14       $884.2394   $884.24   $884.25   $884.30