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 $231.48   5.512%   $244.2392   $244.24   $244.25   $244.20  
  Purchase #2 $210.90   11.142%   $234.3985   $234.40   $234.40   $234.40  
  Purchase #3 $250.92   7.533%   $269.8218   $269.82   $269.80   $269.80  
  Purchase #4 $98.47   10.262%   $108.575   $108.58   $108.60   $108.60  
  Purchase #5 $226.42   5.636%   $239.181   $239.18   $239.20   $239.20  
  Purchase #6 $228.81   3.807%   $237.5208   $237.52   $237.50   $237.50  
  Purchase #7 $147.94   7.135%   $158.4955   $158.50   $158.50   $158.50  
  7 purchase totals = $1,394.94       $1,492.2318   $1,492.24   $1,492.25   $1,492.20