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 $113.32   3.117%   $116.8522   $116.85   $116.85   $116.90  
  Purchase #2 $245.67   6.749%   $262.2503   $262.25   $262.25   $262.30  
  Purchase #3 $33.35   9.732%   $36.5956   $36.60   $36.60   $36.60  
  Purchase #4 $153.84   3.344%   $158.9844   $158.98   $159.00   $159.00  
  Purchase #5 $97.40   11.694%   $108.79   $108.79   $108.80   $108.80  
  Purchase #6 $109.65   3.612%   $113.6106   $113.61   $113.60   $113.60  
  Purchase #7 $65.63   8.663%   $71.3155   $71.32   $71.30   $71.30  
  7 purchase totals = $818.86       $868.3986   $868.40   $868.40   $868.50