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 $246.34   6.420%   $262.155   $262.16   $262.15   $262.20  
  Purchase #2 $135.82   5.250%   $142.9506   $142.95   $142.95   $143.00  
  Purchase #3 $158.31   8.456%   $171.6967   $171.70   $171.70   $171.70  
  Purchase #4 $238.80   11.596%   $266.4912   $266.49   $266.50   $266.50  
  Purchase #5 $62.95   8.325%   $68.1906   $68.19   $68.20   $68.20  
  Purchase #6 $163.98   6.805%   $175.1388   $175.14   $175.15   $175.10  
  Purchase #7 $217.62   3.367%   $224.9473   $224.95   $224.95   $224.90  
  7 purchase totals = $1,223.82       $1,311.5702   $1,311.58   $1,311.60   $1,311.60