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 $210.79   8.268%   $228.2181   $228.22   $228.20   $228.20  
  Purchase #2 $211.60   10.528%   $233.8772   $233.88   $233.90   $233.90  
  Purchase #3 $91.64   10.179%   $100.968   $100.97   $100.95   $101.00  
  Purchase #4 $189.88   8.455%   $205.9344   $205.93   $205.95   $205.90  
  Purchase #5 $231.86   13.551%   $263.2793   $263.28   $263.30   $263.30  
  Purchase #6 $242.81   8.508%   $263.4683   $263.47   $263.45   $263.50  
  Purchase #7 $180.60   8.132%   $195.2864   $195.29   $195.30   $195.30  
  7 purchase totals = $1,359.18       $1,491.0317   $1,491.04   $1,491.05   $1,491.10