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 $23.53   11.584%   $26.2557   $26.26   $26.25   $26.30  
  Purchase #2 $199.92   3.578%   $207.0731   $207.07   $207.05   $207.10  
  Purchase #3 $134.84   6.731%   $143.9161   $143.92   $143.90   $143.90  
  Purchase #4 $42.65   9.871%   $46.86   $46.86   $46.85   $46.90  
  Purchase #5 $111.80   6.862%   $119.4717   $119.47   $119.45   $119.50  
  Purchase #6 $70.55   7.668%   $75.9598   $75.96   $75.95   $76.00  
  Purchase #7 $129.53   11.759%   $144.7614   $144.76   $144.75   $144.80  
  7 purchase totals = $712.82       $764.2978   $764.30   $764.20   $764.50