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 $110.84   7.347%   $118.9834   $118.98   $119.00   $119.00  
  Purchase #2 $227.85   8.225%   $246.5907   $246.59   $246.60   $246.60  
  Purchase #3 $243.60   3.370%   $251.8093   $251.81   $251.80   $251.80  
  Purchase #4 $224.74   4.105%   $233.9656   $233.97   $233.95   $234.00  
  Purchase #5 $248.35   8.177%   $268.6576   $268.66   $268.65   $268.70  
  Purchase #6 $220.99   12.531%   $248.6823   $248.68   $248.70   $248.70  
  Purchase #7 $149.73   5.672%   $158.2227   $158.22   $158.20   $158.20  
  7 purchase totals = $1,426.10       $1,526.9116   $1,526.91   $1,526.90   $1,527.00