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 $68.55   6.138%   $72.7576   $72.76   $72.75   $72.80  
  Purchase #2 $126.26   3.613%   $130.8218   $130.82   $130.80   $130.80  
  Purchase #3 $11.34   5.829%   $12.001   $12.00   $12.00   $12.00  
  Purchase #4 $128.25   5.618%   $135.4551   $135.46   $135.45   $135.50  
  Purchase #5 $184.44   8.535%   $200.182   $200.18   $200.20   $200.20  
  Purchase #6 $158.88   5.771%   $168.049   $168.05   $168.05   $168.00  
  Purchase #7 $45.90   11.821%   $51.3258   $51.33   $51.35   $51.30  
  7 purchase totals = $723.62       $770.5923   $770.60   $770.60   $770.60