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 $53.62   13.342%   $60.774   $60.77   $60.75   $60.80  
  Purchase #2 $162.66   6.427%   $173.1142   $173.11   $173.10   $173.10  
  Purchase #3 $40.95   11.412%   $45.6232   $45.62   $45.60   $45.60  
  Purchase #4 $223.48   8.578%   $242.6501   $242.65   $242.65   $242.70  
  Purchase #5 $48.64   4.449%   $50.804   $50.80   $50.80   $50.80  
  Purchase #6 $37.73   13.727%   $42.9092   $42.91   $42.90   $42.90  
  Purchase #7 $14.26   13.186%   $16.1403   $16.14   $16.15   $16.10  
  7 purchase totals = $581.34       $632.0150   $632.00   $631.95   $632.00