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 $224.48   12.517%   $252.5782   $252.58   $252.60   $252.60  
  Purchase #2 $179.89   3.374%   $185.9595   $185.96   $185.95   $186.00  
  Purchase #3 $64.40   10.712%   $71.2985   $71.30   $71.30   $71.30  
  Purchase #4 $67.44   8.548%   $73.2048   $73.20   $73.20   $73.20  
  Purchase #5 $214.62   4.763%   $224.8424   $224.84   $224.85   $224.80  
  Purchase #6 $217.26   5.389%   $228.9681   $228.97   $228.95   $229.00  
  Purchase #7 $147.27   11.664%   $164.4476   $164.45   $164.45   $164.40  
  7 purchase totals = $1,115.36       $1,201.2991   $1,201.30   $1,201.30   $1,201.30