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 $196.94   13.655%   $223.8322   $223.83   $223.85   $223.80  
  Purchase #2 $240.63   9.340%   $263.1048   $263.10   $263.10   $263.10  
  Purchase #3 $51.37   4.216%   $53.5358   $53.54   $53.55   $53.50  
  Purchase #4 $50.74   9.171%   $55.3934   $55.39   $55.40   $55.40  
  Purchase #5 $69.28   10.534%   $76.578   $76.58   $76.60   $76.60  
  Purchase #6 $27.62   6.584%   $29.4385   $29.44   $29.45   $29.40  
  Purchase #7 $93.48   8.589%   $101.509   $101.51   $101.50   $101.50  
  7 purchase totals = $730.06       $803.3917   $803.39   $803.45   $803.30