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 $83.63   13.418%   $94.8515   $94.85   $94.85   $94.90  
  Purchase #2 $119.97   3.588%   $124.2745   $124.27   $124.25   $124.30  
  Purchase #3 $171.65   6.411%   $182.6545   $182.65   $182.65   $182.70  
  Purchase #4 $22.26   10.786%   $24.661   $24.66   $24.65   $24.70  
  Purchase #5 $51.76   5.199%   $54.451   $54.45   $54.45   $54.50  
  Purchase #6 $132.61   7.834%   $142.9987   $143.00   $143.00   $143.00  
  Purchase #7 $155.39   8.466%   $168.5453   $168.55   $168.55   $168.50  
  7 purchase totals = $737.27       $792.4365   $792.43   $792.40   $792.60