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 $85.63   3.415%   $88.5543   $88.55   $88.55   $88.60  
  Purchase #2 $66.84   7.295%   $71.716   $71.72   $71.70   $71.70  
  Purchase #3 $60.78   4.425%   $63.4695   $63.47   $63.45   $63.50  
  Purchase #4 $91.45   3.249%   $94.4212   $94.42   $94.40   $94.40  
  Purchase #5 $94.65   8.785%   $102.965   $102.97   $102.95   $103.00  
  Purchase #6 $80.76   7.256%   $86.6199   $86.62   $86.60   $86.60  
  Purchase #7 $165.91   5.443%   $174.9405   $174.94   $174.95   $174.90  
  7 purchase totals = $646.02       $682.6864   $682.69   $682.60   $682.70