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 $147.63   13.119%   $166.9976   $167.00   $167.00   $167.00  
  Purchase #2 $180.93   8.800%   $196.8518   $196.85   $196.85   $196.90  
  Purchase #3 $112.70   11.720%   $125.9084   $125.91   $125.90   $125.90  
  Purchase #4 $250.48   7.332%   $268.8452   $268.85   $268.85   $268.80  
  Purchase #5 $72.91   6.294%   $77.499   $77.50   $77.50   $77.50  
  Purchase #6 $105.99   12.534%   $119.2748   $119.27   $119.25   $119.30  
  Purchase #7 $130.33   7.694%   $140.3576   $140.36   $140.35   $140.40  
  7 purchase totals = $1,000.97       $1,095.7344   $1,095.74   $1,095.70   $1,095.80