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 $192.59   10.841%   $213.4687   $213.47   $213.45   $213.50  
  Purchase #2 $166.42   13.418%   $188.7502   $188.75   $188.75   $188.80  
  Purchase #3 $136.35   10.685%   $150.919   $150.92   $150.90   $150.90  
  Purchase #4 $87.90   6.168%   $93.3217   $93.32   $93.30   $93.30  
  Purchase #5 $207.87   11.249%   $231.2533   $231.25   $231.25   $231.30  
  Purchase #6 $215.63   13.125%   $243.9314   $243.93   $243.95   $243.90  
  Purchase #7 $126.34   5.478%   $133.2609   $133.26   $133.25   $133.30  
  7 purchase totals = $1,133.10       $1,254.9052   $1,254.90   $1,254.85   $1,255.00