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 $65.93   5.302%   $69.4256   $69.43   $69.45   $69.40  
  Purchase #2 $213.25   12.282%   $239.4414   $239.44   $239.45   $239.40  
  Purchase #3 $62.61   6.797%   $66.8656   $66.87   $66.85   $66.90  
  Purchase #4 $153.89   12.744%   $173.5017   $173.50   $173.50   $173.50  
  Purchase #5 $168.27   6.420%   $179.0729   $179.07   $179.05   $179.10  
  Purchase #6 $17.54   4.826%   $18.3865   $18.39   $18.40   $18.40  
  Purchase #7 $113.95   13.282%   $129.0848   $129.08   $129.10   $129.10  
  7 purchase totals = $795.44       $875.7785   $875.78   $875.80   $875.80