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 $203.43   5.188%   $213.9839   $213.98   $214.00   $214.00  
  Purchase #2 $37.99   8.514%   $41.2245   $41.22   $41.20   $41.20  
  Purchase #3 $238.93   10.871%   $264.9041   $264.90   $264.90   $264.90  
  Purchase #4 $199.51   3.564%   $206.6205   $206.62   $206.60   $206.60  
  Purchase #5 $57.32   6.248%   $60.9014   $60.90   $60.90   $60.90  
  Purchase #6 $179.63   10.699%   $198.8486   $198.85   $198.85   $198.80  
  Purchase #7 $44.72   11.547%   $49.8838   $49.88   $49.90   $49.90  
  7 purchase totals = $961.53       $1,036.3668   $1,036.35   $1,036.35   $1,036.30