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 $73.66   13.556%   $83.6453   $83.65   $83.65   $83.60  
  Purchase #2 $212.26   6.251%   $225.5284   $225.53   $225.55   $225.50  
  Purchase #3 $103.27   11.576%   $115.2245   $115.22   $115.20   $115.20  
  Purchase #4 $242.26   8.772%   $263.511   $263.51   $263.50   $263.50  
  Purchase #5 $61.72   11.802%   $69.0042   $69.00   $69.00   $69.00  
  Purchase #6 $96.73   4.826%   $101.3982   $101.40   $101.40   $101.40  
  Purchase #7 $98.78   8.817%   $107.4894   $107.49   $107.50   $107.50  
  7 purchase totals = $888.68       $965.8010   $965.80   $965.80   $965.70