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 $35.63   8.477%   $38.6504   $38.65   $38.65   $38.70  
  Purchase #2 $243.69   6.688%   $259.988   $259.99   $260.00   $260.00  
  Purchase #3 $66.43   13.699%   $75.5302   $75.53   $75.55   $75.50  
  Purchase #4 $171.39   6.191%   $182.0008   $182.00   $182.00   $182.00  
  Purchase #5 $60.40   3.327%   $62.4095   $62.41   $62.40   $62.40  
  Purchase #6 $199.39   8.744%   $216.8247   $216.82   $216.80   $216.80  
  Purchase #7 $211.36   9.567%   $231.5808   $231.58   $231.60   $231.60  
  7 purchase totals = $988.29       $1,066.9844   $1,066.98   $1,067.00   $1,067.00