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 $49.81   10.786%   $55.1825   $55.18   $55.20   $55.20  
  Purchase #2 $244.35   13.865%   $278.2291   $278.23   $278.25   $278.20  
  Purchase #3 $152.71   3.700%   $158.3603   $158.36   $158.35   $158.40  
  Purchase #4 $95.35   12.201%   $106.9837   $106.98   $107.00   $107.00  
  Purchase #5 $72.49   3.478%   $75.0112   $75.01   $75.00   $75.00  
  Purchase #6 $80.49   7.478%   $86.509   $86.51   $86.50   $86.50  
  Purchase #7 $191.91   6.314%   $204.0272   $204.03   $204.05   $204.00  
  7 purchase totals = $887.11       $964.3030   $964.30   $964.35   $964.30