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 $246.27   8.230%   $266.538   $266.54   $266.55   $266.50  
  Purchase #2 $215.38   4.248%   $224.5293   $224.53   $224.55   $224.50  
  Purchase #3 $40.87   7.762%   $44.0423   $44.04   $44.05   $44.00  
  Purchase #4 $60.63   8.441%   $65.7478   $65.75   $65.75   $65.70  
  Purchase #5 $204.44   10.826%   $226.5727   $226.57   $226.55   $226.60  
  Purchase #6 $39.46   10.273%   $43.5137   $43.51   $43.50   $43.50  
  Purchase #7 $108.85   8.635%   $118.2492   $118.25   $118.25   $118.20  
  7 purchase totals = $915.90       $989.1930   $989.19   $989.20   $989.00