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 $19.49   11.700%   $21.7703   $21.77   $21.75   $21.80  
  Purchase #2 $131.64   5.679%   $139.1158   $139.12   $139.10   $139.10  
  Purchase #3 $10.79   3.269%   $11.1427   $11.14   $11.15   $11.10  
  Purchase #4 $185.88   12.390%   $208.9105   $208.91   $208.90   $208.90  
  Purchase #5 $211.46   8.775%   $230.0156   $230.02   $230.00   $230.00  
  Purchase #6 $36.54   5.264%   $38.4635   $38.46   $38.45   $38.50  
  Purchase #7 $184.90   6.311%   $196.569   $196.57   $196.55   $196.60  
  7 purchase totals = $780.70       $845.9874   $845.99   $845.90   $846.00