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 $206.87   3.808%   $214.7476   $214.75   $214.75   $214.70  
  Purchase #2 $75.91   3.694%   $78.7141   $78.71   $78.70   $78.70  
  Purchase #3 $201.49   11.293%   $224.2443   $224.24   $224.25   $224.20  
  Purchase #4 $201.27   4.322%   $209.9689   $209.97   $209.95   $210.00  
  Purchase #5 $10.25   3.471%   $10.6058   $10.61   $10.60   $10.60  
  Purchase #6 $140.47   8.805%   $152.8384   $152.84   $152.85   $152.80  
  Purchase #7 $35.97   10.321%   $39.6825   $39.68   $39.70   $39.70  
  7 purchase totals = $872.23       $930.8016   $930.80   $930.80   $930.70