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 $57.58   5.211%   $60.5805   $60.58   $60.60   $60.60  
  Purchase #2 $160.60   13.411%   $182.1381   $182.14   $182.15   $182.10  
  Purchase #3 $208.29   7.342%   $223.5827   $223.58   $223.60   $223.60  
  Purchase #4 $49.51   12.648%   $55.772   $55.77   $55.75   $55.80  
  Purchase #5 $70.37   7.205%   $75.4402   $75.44   $75.45   $75.40  
  Purchase #6 $24.58   4.575%   $25.7045   $25.70   $25.70   $25.70  
  Purchase #7 $246.87   4.786%   $258.6852   $258.69   $258.70   $258.70  
  7 purchase totals = $817.80       $881.9032   $881.90   $881.95   $881.90