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 $88.63   11.646%   $98.9518   $98.95   $98.95   $99.00  
  Purchase #2 $43.79   5.584%   $46.2352   $46.24   $46.25   $46.20  
  Purchase #3 $131.44   8.590%   $142.7307   $142.73   $142.75   $142.70  
  Purchase #4 $160.57   4.744%   $168.1874   $168.19   $168.20   $168.20  
  Purchase #5 $171.50   4.747%   $179.6411   $179.64   $179.65   $179.60  
  Purchase #6 $236.99   6.375%   $252.0981   $252.10   $252.10   $252.10  
  Purchase #7 $134.48   8.399%   $145.775   $145.78   $145.80   $145.80  
  7 purchase totals = $967.40       $1,033.6193   $1,033.63   $1,033.70   $1,033.60