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 $244.66   8.807%   $266.2072   $266.21   $266.20   $266.20  
  Purchase #2 $50.47   6.205%   $53.6017   $53.60   $53.60   $53.60  
  Purchase #3 $83.67   5.477%   $88.2526   $88.25   $88.25   $88.30  
  Purchase #4 $48.78   8.356%   $52.8561   $52.86   $52.85   $52.90  
  Purchase #5 $88.45   13.259%   $100.1776   $100.18   $100.20   $100.20  
  Purchase #6 $192.84   4.349%   $201.2266   $201.23   $201.25   $201.20  
  Purchase #7 $68.84   12.291%   $77.3011   $77.30   $77.30   $77.30  
  7 purchase totals = $777.71       $839.6229   $839.63   $839.65   $839.70