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 $200.63   11.764%   $224.2321   $224.23   $224.25   $224.20  
  Purchase #2 $241.52   10.617%   $267.1622   $267.16   $267.15   $267.20  
  Purchase #3 $89.80   6.682%   $95.8004   $95.80   $95.80   $95.80  
  Purchase #4 $62.41   13.634%   $70.919   $70.92   $70.90   $70.90  
  Purchase #5 $194.72   5.435%   $205.303   $205.30   $205.30   $205.30  
  Purchase #6 $116.29   5.787%   $123.0197   $123.02   $123.00   $123.00  
  Purchase #7 $208.81   10.603%   $230.9501   $230.95   $230.95   $231.00  
  7 purchase totals = $1,114.18       $1,217.3865   $1,217.38   $1,217.35   $1,217.40