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 $107.74   11.126%   $119.7272   $119.73   $119.75   $119.70  
  Purchase #2 $156.43   12.259%   $175.6068   $175.61   $175.60   $175.60  
  Purchase #3 $37.62   12.747%   $42.4154   $42.42   $42.40   $42.40  
  Purchase #4 $210.26   4.871%   $220.5018   $220.50   $220.50   $220.50  
  Purchase #5 $187.44   13.160%   $212.1071   $212.11   $212.10   $212.10  
  Purchase #6 $183.87   6.789%   $196.3529   $196.35   $196.35   $196.40  
  Purchase #7 $73.58   10.629%   $81.4008   $81.40   $81.40   $81.40  
  7 purchase totals = $956.94       $1,048.1120   $1,048.12   $1,048.10   $1,048.10