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 $19.95   13.275%   $22.5984   $22.60   $22.60   $22.60  
  Purchase #2 $84.32   12.214%   $94.6188   $94.62   $94.60   $94.60  
  Purchase #3 $95.80   6.129%   $101.6716   $101.67   $101.65   $101.70  
  Purchase #4 $168.43   11.818%   $188.3351   $188.34   $188.35   $188.30  
  Purchase #5 $134.69   5.495%   $142.0912   $142.09   $142.10   $142.10  
  Purchase #6 $183.39   6.459%   $195.2352   $195.24   $195.25   $195.20  
  Purchase #7 $15.39   8.470%   $16.6935   $16.69   $16.70   $16.70  
  7 purchase totals = $701.97       $761.2438   $761.25   $761.25   $761.20