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 $88.55   6.674%   $94.4598   $94.46   $94.45   $94.50  
  Purchase #2 $109.70   3.547%   $113.5911   $113.59   $113.60   $113.60  
  Purchase #3 $105.48   12.113%   $118.2568   $118.26   $118.25   $118.30  
  Purchase #4 $239.26   10.224%   $263.7219   $263.72   $263.70   $263.70  
  Purchase #5 $242.71   9.261%   $265.1874   $265.19   $265.20   $265.20  
  Purchase #6 $48.73   10.185%   $53.6932   $53.69   $53.70   $53.70  
  Purchase #7 $247.41   4.694%   $259.0234   $259.02   $259.00   $259.00  
  7 purchase totals = $1,081.84       $1,167.9336   $1,167.93   $1,167.90   $1,168.00