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 $228.86   6.196%   $243.0402   $243.04   $243.05   $243.00  
  Purchase #2 $219.44   3.337%   $226.7627   $226.76   $226.75   $226.80  
  Purchase #3 $117.84   10.755%   $130.5137   $130.51   $130.50   $130.50  
  Purchase #4 $179.29   3.185%   $185.0004   $185.00   $185.00   $185.00  
  Purchase #5 $198.77   13.785%   $226.1704   $226.17   $226.15   $226.20  
  Purchase #6 $87.91   5.221%   $92.4998   $92.50   $92.50   $92.50  
  Purchase #7 $90.83   8.112%   $98.1981   $98.20   $98.20   $98.20  
  7 purchase totals = $1,122.94       $1,202.1853   $1,202.18   $1,202.15   $1,202.20