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 $185.31   11.611%   $206.8263   $206.83   $206.85   $206.80  
  Purchase #2 $192.73   10.373%   $212.7219   $212.72   $212.70   $212.70  
  Purchase #3 $221.95   3.562%   $229.8559   $229.86   $229.85   $229.90  
  Purchase #4 $84.99   4.273%   $88.6216   $88.62   $88.60   $88.60  
  Purchase #5 $249.49   10.497%   $275.679   $275.68   $275.70   $275.70  
  Purchase #6 $68.34   7.537%   $73.4908   $73.49   $73.50   $73.50  
  Purchase #7 $107.31   6.535%   $114.3227   $114.32   $114.30   $114.30  
  7 purchase totals = $1,110.12       $1,201.5182   $1,201.52   $1,201.50   $1,201.50