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 $44.92   13.104%   $50.8063   $50.81   $50.80   $50.80  
  Purchase #2 $205.41   6.242%   $218.2317   $218.23   $218.25   $218.20  
  Purchase #3 $47.63   5.819%   $50.4016   $50.40   $50.40   $50.40  
  Purchase #4 $246.70   13.255%   $279.4001   $279.40   $279.40   $279.40  
  Purchase #5 $38.40   6.416%   $40.8637   $40.86   $40.85   $40.90  
  Purchase #6 $118.88   12.381%   $133.5985   $133.60   $133.60   $133.60  
  Purchase #7 $233.61   12.163%   $262.024   $262.02   $262.00   $262.00  
  7 purchase totals = $935.55       $1,035.3259   $1,035.32   $1,035.30   $1,035.30