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 $246.86   6.217%   $262.2073   $262.21   $262.20   $262.20  
  Purchase #2 $228.98   11.234%   $254.7036   $254.70   $254.70   $254.70  
  Purchase #3 $183.44   12.336%   $206.0692   $206.07   $206.05   $206.10  
  Purchase #4 $38.42   11.427%   $42.8103   $42.81   $42.80   $42.80  
  Purchase #5 $29.79   4.723%   $31.197   $31.20   $31.20   $31.20  
  Purchase #6 $249.90   12.467%   $281.055   $281.06   $281.05   $281.10  
  Purchase #7 $206.30   11.383%   $229.7831   $229.78   $229.80   $229.80  
  7 purchase totals = $1,183.69       $1,307.8255   $1,307.83   $1,307.80   $1,307.90