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 $47.82   12.521%   $53.8075   $53.81   $53.80   $53.80  
  Purchase #2 $136.95   11.799%   $153.1087   $153.11   $153.10   $153.10  
  Purchase #3 $167.65   8.571%   $182.0193   $182.02   $182.00   $182.00  
  Purchase #4 $26.45   13.143%   $29.9263   $29.93   $29.95   $29.90  
  Purchase #5 $56.81   5.852%   $60.1345   $60.13   $60.15   $60.10  
  Purchase #6 $42.31   9.416%   $46.2939   $46.29   $46.30   $46.30  
  Purchase #7 $182.39   5.361%   $192.1679   $192.17   $192.15   $192.20  
  7 purchase totals = $660.38       $717.4581   $717.46   $717.45   $717.40