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 $125.72   12.419%   $141.3332   $141.33   $141.35   $141.30  
  Purchase #2 $24.72   5.150%   $25.9931   $25.99   $26.00   $26.00  
  Purchase #3 $39.75   3.850%   $41.2804   $41.28   $41.30   $41.30  
  Purchase #4 $244.97   4.566%   $256.1553   $256.16   $256.15   $256.20  
  Purchase #5 $226.83   5.742%   $239.8546   $239.85   $239.85   $239.90  
  Purchase #6 $189.97   13.136%   $214.9245   $214.92   $214.90   $214.90  
  Purchase #7 $31.36   7.130%   $33.596   $33.60   $33.60   $33.60  
  7 purchase totals = $883.32       $953.1371   $953.13   $953.15   $953.20