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 $170.48   7.146%   $182.6625   $182.66   $182.65   $182.70  
  Purchase #2 $215.82   6.503%   $229.8548   $229.85   $229.85   $229.90  
  Purchase #3 $113.43   3.381%   $117.2651   $117.27   $117.25   $117.30  
  Purchase #4 $213.32   11.521%   $237.8966   $237.90   $237.90   $237.90  
  Purchase #5 $207.61   7.802%   $223.8077   $223.81   $223.80   $223.80  
  Purchase #6 $98.64   8.332%   $106.8587   $106.86   $106.85   $106.90  
  Purchase #7 $60.33   10.842%   $66.871   $66.87   $66.85   $66.90  
  7 purchase totals = $1,079.63       $1,165.2164   $1,165.22   $1,165.15   $1,165.40