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 $68.42   6.824%   $73.089   $73.09   $73.10   $73.10  
  Purchase #2 $79.52   8.778%   $86.5003   $86.50   $86.50   $86.50  
  Purchase #3 $23.71   4.176%   $24.7001   $24.70   $24.70   $24.70  
  Purchase #4 $135.56   13.298%   $153.5868   $153.59   $153.60   $153.60  
  Purchase #5 $99.62   8.482%   $108.0698   $108.07   $108.05   $108.10  
  Purchase #6 $241.59   12.727%   $272.3372   $272.34   $272.35   $272.30  
  Purchase #7 $89.67   3.129%   $92.4758   $92.48   $92.50   $92.50  
  7 purchase totals = $738.09       $810.7590   $810.77   $810.80   $810.80