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 $96.38   10.516%   $106.5153   $106.52   $106.50   $106.50  
  Purchase #2 $161.99   4.121%   $168.6656   $168.67   $168.65   $168.70  
  Purchase #3 $37.56   7.199%   $40.2639   $40.26   $40.25   $40.30  
  Purchase #4 $242.81   12.341%   $272.7752   $272.78   $272.80   $272.80  
  Purchase #5 $61.31   4.727%   $64.2081   $64.21   $64.20   $64.20  
  Purchase #6 $238.53   11.727%   $266.5024   $266.50   $266.50   $266.50  
  Purchase #7 $124.33   5.111%   $130.6845   $130.68   $130.70   $130.70  
  7 purchase totals = $962.91       $1,049.6150   $1,049.62   $1,049.60   $1,049.70