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 $214.42   12.356%   $240.9137   $240.91   $240.90   $240.90  
  Purchase #2 $185.43   12.742%   $209.0575   $209.06   $209.05   $209.10  
  Purchase #3 $242.32   3.667%   $251.2059   $251.21   $251.20   $251.20  
  Purchase #4 $10.94   12.776%   $12.3377   $12.34   $12.35   $12.30  
  Purchase #5 $250.87   6.406%   $266.9407   $266.94   $266.95   $266.90  
  Purchase #6 $131.47   13.707%   $149.4906   $149.49   $149.50   $149.50  
  Purchase #7 $248.45   13.490%   $281.9659   $281.97   $281.95   $282.00  
  7 purchase totals = $1,283.90       $1,411.9120   $1,411.92   $1,411.90   $1,411.90