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 $59.73   8.516%   $64.8166   $64.82   $64.80   $64.80  
  Purchase #2 $7.56   5.229%   $7.9553   $7.96   $7.95   $8.00  
  Purchase #3 $28.40   4.700%   $29.7348   $29.73   $29.75   $29.70  
  Purchase #4 $192.25   3.527%   $199.0307   $199.03   $199.05   $199.00  
  Purchase #5 $187.91   6.173%   $199.5097   $199.51   $199.50   $199.50  
  Purchase #6 $201.91   11.728%   $225.59   $225.59   $225.60   $225.60  
  Purchase #7 $141.48   11.737%   $158.0855   $158.09   $158.10   $158.10  
  7 purchase totals = $819.24       $884.7226   $884.73   $884.75   $884.70