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 $114.62   5.540%   $120.9699   $120.97   $120.95   $121.00  
  Purchase #2 $247.94   9.553%   $271.6257   $271.63   $271.65   $271.60  
  Purchase #3 $227.57   11.136%   $252.9122   $252.91   $252.90   $252.90  
  Purchase #4 $88.66   6.552%   $94.469   $94.47   $94.45   $94.50  
  Purchase #5 $108.26   4.801%   $113.4576   $113.46   $113.45   $113.50  
  Purchase #6 $166.25   5.828%   $175.9391   $175.94   $175.95   $175.90  
  Purchase #7 $177.57   7.114%   $190.2023   $190.20   $190.20   $190.20  
  7 purchase totals = $1,130.87       $1,219.5758   $1,219.58   $1,219.55   $1,219.60