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 $7.41   3.838%   $7.6944   $7.69   $7.70   $7.70  
  Purchase #2 $139.34   6.209%   $147.9916   $147.99   $148.00   $148.00  
  Purchase #3 $179.71   6.345%   $191.1126   $191.11   $191.10   $191.10  
  Purchase #4 $16.36   4.495%   $17.0954   $17.10   $17.10   $17.10  
  Purchase #5 $146.42   9.511%   $160.346   $160.35   $160.35   $160.30  
  Purchase #6 $31.56   13.117%   $35.6997   $35.70   $35.70   $35.70  
  Purchase #7 $42.55   10.662%   $47.0867   $47.09   $47.10   $47.10  
  7 purchase totals = $563.35       $607.0264   $607.03   $607.05   $607.00