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 $57.58   13.613%   $65.4184   $65.42   $65.40   $65.40  
  Purchase #2 $237.90   10.371%   $262.5726   $262.57   $262.55   $262.60  
  Purchase #3 $12.92   9.155%   $14.1028   $14.10   $14.10   $14.10  
  Purchase #4 $138.81   10.366%   $153.199   $153.20   $153.20   $153.20  
  Purchase #5 $199.50   6.577%   $212.6211   $212.62   $212.60   $212.60  
  Purchase #6 $110.49   6.751%   $117.9492   $117.95   $117.95   $117.90  
  Purchase #7 $37.54   10.298%   $41.4059   $41.41   $41.40   $41.40  
  7 purchase totals = $794.74       $867.2690   $867.27   $867.20   $867.20