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 $86.51   12.534%   $97.3532   $97.35   $97.35   $97.40  
  Purchase #2 $168.27   3.135%   $173.5453   $173.55   $173.55   $173.50  
  Purchase #3 $59.28   12.412%   $66.6378   $66.64   $66.65   $66.60  
  Purchase #4 $64.34   11.381%   $71.6625   $71.66   $71.65   $71.70  
  Purchase #5 $152.89   6.642%   $163.045   $163.05   $163.05   $163.00  
  Purchase #6 $112.70   4.143%   $117.3692   $117.37   $117.35   $117.40  
  Purchase #7 $84.68   11.376%   $94.3132   $94.31   $94.30   $94.30  
  7 purchase totals = $728.67       $783.9262   $783.93   $783.90   $783.90