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 $120.64   8.191%   $130.5216   $130.52   $130.50   $130.50  
  Purchase #2 $23.47   13.339%   $26.6007   $26.60   $26.60   $26.60  
  Purchase #3 $39.66   4.386%   $41.3995   $41.40   $41.40   $41.40  
  Purchase #4 $52.97   12.692%   $59.693   $59.69   $59.70   $59.70  
  Purchase #5 $94.86   3.551%   $98.2285   $98.23   $98.25   $98.20  
  Purchase #6 $150.25   7.178%   $161.0349   $161.03   $161.05   $161.00  
  Purchase #7 $217.29   4.249%   $226.5227   $226.52   $226.50   $226.50  
  7 purchase totals = $699.14       $744.0009   $743.99   $744.00   $743.90