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 $116.92   8.547%   $126.9132   $126.91   $126.90   $126.90  
  Purchase #2 $124.77   12.283%   $140.0955   $140.10   $140.10   $140.10  
  Purchase #3 $230.66   8.785%   $250.9235   $250.92   $250.90   $250.90  
  Purchase #4 $177.31   10.395%   $195.7414   $195.74   $195.75   $195.70  
  Purchase #5 $161.77   13.476%   $183.5701   $183.57   $183.55   $183.60  
  Purchase #6 $64.31   8.808%   $69.9744   $69.97   $69.95   $70.00  
  Purchase #7 $60.83   8.655%   $66.0948   $66.09   $66.10   $66.10  
  7 purchase totals = $936.57       $1,033.3129   $1,033.30   $1,033.25   $1,033.30