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 $236.88   3.864%   $246.033   $246.03   $246.05   $246.00  
  Purchase #2 $162.49   12.519%   $182.8321   $182.83   $182.85   $182.80  
  Purchase #3 $22.43   11.460%   $25.0005   $25.00   $25.00   $25.00  
  Purchase #4 $12.90   12.698%   $14.538   $14.54   $14.55   $14.50  
  Purchase #5 $7.43   4.616%   $7.773   $7.77   $7.75   $7.80  
  Purchase #6 $195.45   9.795%   $214.5943   $214.59   $214.60   $214.60  
  Purchase #7 $161.90   4.416%   $169.0495   $169.05   $169.05   $169.00  
  7 purchase totals = $799.48       $859.8204   $859.81   $859.85   $859.70