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 $167.79   13.541%   $190.5104   $190.51   $190.50   $190.50  
  Purchase #2 $27.72   11.469%   $30.8992   $30.90   $30.90   $30.90  
  Purchase #3 $171.69   8.749%   $186.7112   $186.71   $186.70   $186.70  
  Purchase #4 $112.39   13.628%   $127.7065   $127.71   $127.70   $127.70  
  Purchase #5 $219.36   4.523%   $229.2817   $229.28   $229.30   $229.30  
  Purchase #6 $46.54   7.475%   $50.0189   $50.02   $50.00   $50.00  
  Purchase #7 $192.80   13.109%   $218.0742   $218.07   $218.05   $218.10  
  7 purchase totals = $938.29       $1,033.2021   $1,033.20   $1,033.15   $1,033.20