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 $176.74   5.660%   $186.7435   $186.74   $186.75   $186.70  
  Purchase #2 $98.99   5.592%   $104.5255   $104.53   $104.55   $104.50  
  Purchase #3 $96.30   12.866%   $108.69   $108.69   $108.70   $108.70  
  Purchase #4 $215.56   9.435%   $235.8981   $235.90   $235.90   $235.90  
  Purchase #5 $218.82   9.224%   $239.004   $239.00   $239.00   $239.00  
  Purchase #6 $85.99   12.515%   $96.7516   $96.75   $96.75   $96.80  
  Purchase #7 $66.63   3.183%   $68.7508   $68.75   $68.75   $68.80  
  7 purchase totals = $959.03       $1,040.3635   $1,040.36   $1,040.40   $1,040.40