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 $227.69   4.662%   $238.3049   $238.30   $238.30   $238.30  
  Purchase #2 $240.51   10.828%   $266.5524   $266.55   $266.55   $266.60  
  Purchase #3 $170.79   5.798%   $180.6924   $180.69   $180.70   $180.70  
  Purchase #4 $240.91   5.742%   $254.7431   $254.74   $254.75   $254.70  
  Purchase #5 $48.52   13.856%   $55.2429   $55.24   $55.25   $55.20  
  Purchase #6 $167.52   13.396%   $189.961   $189.96   $189.95   $190.00  
  Purchase #7 $149.70   5.502%   $157.9365   $157.94   $157.95   $157.90  
  7 purchase totals = $1,245.64       $1,343.4332   $1,343.42   $1,343.45   $1,343.40