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 $117.32   12.466%   $131.9451   $131.95   $131.95   $131.90  
  Purchase #2 $163.86   10.662%   $181.3308   $181.33   $181.35   $181.30  
  Purchase #3 $13.53   10.602%   $14.9645   $14.96   $14.95   $15.00  
  Purchase #4 $120.28   6.566%   $128.1776   $128.18   $128.20   $128.20  
  Purchase #5 $235.88   3.427%   $243.9636   $243.96   $243.95   $244.00  
  Purchase #6 $60.31   8.779%   $65.6046   $65.60   $65.60   $65.60  
  Purchase #7 $219.36   5.531%   $231.4928   $231.49   $231.50   $231.50  
  7 purchase totals = $930.54       $997.4790   $997.47   $997.50   $997.50