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 $200.59   11.661%   $223.9808   $223.98   $224.00   $224.00  
  Purchase #2 $68.55   10.124%   $75.49   $75.49   $75.50   $75.50  
  Purchase #3 $152.47   10.668%   $168.7355   $168.74   $168.75   $168.70  
  Purchase #4 $14.30   7.608%   $15.3879   $15.39   $15.40   $15.40  
  Purchase #5 $26.64   11.707%   $29.7587   $29.76   $29.75   $29.80  
  Purchase #6 $221.62   10.452%   $244.7837   $244.78   $244.80   $244.80  
  Purchase #7 $141.87   11.472%   $158.1453   $158.15   $158.15   $158.10  
  7 purchase totals = $826.04       $916.2819   $916.29   $916.35   $916.30