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 $242.99   11.777%   $271.6069   $271.61   $271.60   $271.60  
  Purchase #2 $107.67   4.811%   $112.85   $112.85   $112.85   $112.90  
  Purchase #3 $23.31   5.610%   $24.6177   $24.62   $24.60   $24.60  
  Purchase #4 $96.47   12.827%   $108.8442   $108.84   $108.85   $108.80  
  Purchase #5 $68.87   10.128%   $75.8452   $75.85   $75.85   $75.80  
  Purchase #6 $228.45   13.820%   $260.0218   $260.02   $260.00   $260.00  
  Purchase #7 $114.86   5.848%   $121.577   $121.58   $121.60   $121.60  
  7 purchase totals = $882.62       $975.3628   $975.37   $975.35   $975.30