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 $65.65   4.611%   $68.6771   $68.68   $68.70   $68.70  
  Purchase #2 $57.58   8.859%   $62.681   $62.68   $62.70   $62.70  
  Purchase #3 $68.95   9.188%   $75.2851   $75.29   $75.30   $75.30  
  Purchase #4 $250.60   9.282%   $273.8607   $273.86   $273.85   $273.90  
  Purchase #5 $7.74   5.829%   $8.1912   $8.19   $8.20   $8.20  
  Purchase #6 $60.97   9.664%   $66.8621   $66.86   $66.85   $66.90  
  Purchase #7 $211.42   4.846%   $221.6654   $221.67   $221.65   $221.70  
  7 purchase totals = $722.91       $777.2226   $777.23   $777.25   $777.40