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 $101.51   10.693%   $112.3645   $112.36   $112.35   $112.40  
  Purchase #2 $168.86   13.322%   $191.3555   $191.36   $191.35   $191.40  
  Purchase #3 $100.50   10.858%   $111.4123   $111.41   $111.40   $111.40  
  Purchase #4 $231.37   9.694%   $253.799   $253.80   $253.80   $253.80  
  Purchase #5 $223.80   10.802%   $247.9749   $247.97   $247.95   $248.00  
  Purchase #6 $203.29   11.328%   $226.3187   $226.32   $226.30   $226.30  
  Purchase #7 $121.48   8.686%   $132.0318   $132.03   $132.05   $132.00  
  7 purchase totals = $1,150.81       $1,275.2567   $1,275.25   $1,275.20   $1,275.30