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 $62.82   9.670%   $68.8947   $68.89   $68.90   $68.90  
  Purchase #2 $31.34   11.569%   $34.9657   $34.97   $34.95   $35.00  
  Purchase #3 $22.32   9.161%   $24.3647   $24.36   $24.35   $24.40  
  Purchase #4 $211.86   10.873%   $234.8955   $234.90   $234.90   $234.90  
  Purchase #5 $186.30   10.787%   $206.3962   $206.40   $206.40   $206.40  
  Purchase #6 $54.66   4.218%   $56.9656   $56.97   $56.95   $57.00  
  Purchase #7 $16.39   8.225%   $17.7381   $17.74   $17.75   $17.70  
  7 purchase totals = $585.69       $644.2205   $644.23   $644.20   $644.30