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 $41.43   3.419%   $42.8465   $42.85   $42.85   $42.80  
  Purchase #2 $179.48   9.164%   $195.9275   $195.93   $195.95   $195.90  
  Purchase #3 $69.74   9.231%   $76.1777   $76.18   $76.20   $76.20  
  Purchase #4 $82.26   12.180%   $92.2793   $92.28   $92.30   $92.30  
  Purchase #5 $160.71   12.770%   $181.2327   $181.23   $181.25   $181.20  
  Purchase #6 $246.85   4.567%   $258.1236   $258.12   $258.10   $258.10  
  Purchase #7 $36.77   3.860%   $38.1893   $38.19   $38.20   $38.20  
  7 purchase totals = $817.24       $884.7766   $884.78   $884.85   $884.70