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 $53.61   13.811%   $61.0141   $61.01   $61.00   $61.00  
  Purchase #2 $31.57   8.666%   $34.3059   $34.31   $34.30   $34.30  
  Purchase #3 $227.86   7.774%   $245.5738   $245.57   $245.55   $245.60  
  Purchase #4 $35.97   3.632%   $37.2764   $37.28   $37.30   $37.30  
  Purchase #5 $28.58   5.798%   $30.2371   $30.24   $30.25   $30.20  
  Purchase #6 $156.54   12.553%   $176.1905   $176.19   $176.20   $176.20  
  Purchase #7 $126.71   7.731%   $136.506   $136.51   $136.50   $136.50  
  7 purchase totals = $660.84       $721.1038   $721.11   $721.10   $721.10