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 $191.55   11.209%   $213.0208   $213.02   $213.00   $213.00  
  Purchase #2 $127.85   4.823%   $134.0162   $134.02   $134.00   $134.00  
  Purchase #3 $70.65   6.164%   $75.0049   $75.00   $75.00   $75.00  
  Purchase #4 $123.34   11.591%   $137.6363   $137.64   $137.65   $137.60  
  Purchase #5 $126.63   11.767%   $141.5306   $141.53   $141.55   $141.50  
  Purchase #6 $193.60   10.848%   $214.6017   $214.60   $214.60   $214.60  
  Purchase #7 $70.82   12.569%   $79.7214   $79.72   $79.70   $79.70  
  7 purchase totals = $904.44       $995.5319   $995.53   $995.50   $995.40