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 $85.74   11.665%   $95.7416   $95.74   $95.75   $95.70  
  Purchase #2 $198.26   12.228%   $222.5032   $222.50   $222.50   $222.50  
  Purchase #3 $44.76   13.602%   $50.8483   $50.85   $50.85   $50.80  
  Purchase #4 $35.42   11.761%   $39.5857   $39.59   $39.60   $39.60  
  Purchase #5 $70.45   6.545%   $75.061   $75.06   $75.05   $75.10  
  Purchase #6 $115.80   7.488%   $124.4711   $124.47   $124.45   $124.50  
  Purchase #7 $86.52   10.607%   $95.6972   $95.70   $95.70   $95.70  
  7 purchase totals = $636.95       $703.9081   $703.91   $703.90   $703.90