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 $224.99   10.194%   $247.9255   $247.93   $247.95   $247.90  
  Purchase #2 $75.43   8.163%   $81.5874   $81.59   $81.60   $81.60  
  Purchase #3 $32.53   5.332%   $34.2645   $34.26   $34.25   $34.30  
  Purchase #4 $47.44   13.727%   $53.9521   $53.95   $53.95   $54.00  
  Purchase #5 $84.25   4.485%   $88.0286   $88.03   $88.05   $88.00  
  Purchase #6 $120.96   10.314%   $133.4358   $133.44   $133.45   $133.40  
  Purchase #7 $226.86   8.156%   $245.3627   $245.36   $245.35   $245.40  
  7 purchase totals = $812.46       $884.5566   $884.56   $884.60   $884.60