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 $60.54   8.305%   $65.5678   $65.57   $65.55   $65.60  
  Purchase #2 $215.71   6.301%   $229.3019   $229.30   $229.30   $229.30  
  Purchase #3 $184.82   9.383%   $202.1617   $202.16   $202.15   $202.20  
  Purchase #4 $67.62   3.247%   $69.8156   $69.82   $69.80   $69.80  
  Purchase #5 $209.85   6.353%   $223.1818   $223.18   $223.20   $223.20  
  Purchase #6 $198.85   13.277%   $225.2513   $225.25   $225.25   $225.30  
  Purchase #7 $230.44   5.227%   $242.4851   $242.49   $242.50   $242.50  
  7 purchase totals = $1,167.83       $1,257.7652   $1,257.77   $1,257.75   $1,257.90