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 $120.47   5.391%   $126.9645   $126.96   $126.95   $127.00  
  Purchase #2 $78.77   5.240%   $82.8975   $82.90   $82.90   $82.90  
  Purchase #3 $228.48   13.464%   $259.2425   $259.24   $259.25   $259.20  
  Purchase #4 $233.97   9.408%   $255.9819   $255.98   $256.00   $256.00  
  Purchase #5 $59.98   5.632%   $63.3581   $63.36   $63.35   $63.40  
  Purchase #6 $119.31   4.857%   $125.1049   $125.10   $125.10   $125.10  
  Purchase #7 $70.91   7.371%   $76.1368   $76.14   $76.15   $76.10  
  7 purchase totals = $911.89       $989.6862   $989.68   $989.70   $989.70