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 $116.95   11.681%   $130.6109   $130.61   $130.60   $130.60  
  Purchase #2 $117.98   7.489%   $126.8155   $126.82   $126.80   $126.80  
  Purchase #3 $31.80   13.294%   $36.0275   $36.03   $36.05   $36.00  
  Purchase #4 $67.48   3.131%   $69.5928   $69.59   $69.60   $69.60  
  Purchase #5 $233.92   7.795%   $252.1541   $252.15   $252.15   $252.20  
  Purchase #6 $19.97   8.195%   $21.6065   $21.61   $21.60   $21.60  
  Purchase #7 $105.60   13.161%   $119.498   $119.50   $119.50   $119.50  
  7 purchase totals = $693.70       $756.3053   $756.31   $756.30   $756.30