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 $249.54   9.417%   $273.0392   $273.04   $273.05   $273.00  
  Purchase #2 $28.86   4.337%   $30.1117   $30.11   $30.10   $30.10  
  Purchase #3 $239.85   4.261%   $250.07   $250.07   $250.05   $250.10  
  Purchase #4 $57.64   9.334%   $63.0201   $63.02   $63.00   $63.00  
  Purchase #5 $104.37   11.536%   $116.4101   $116.41   $116.40   $116.40  
  Purchase #6 $54.59   13.281%   $61.8401   $61.84   $61.85   $61.80  
  Purchase #7 $215.92   7.248%   $231.5699   $231.57   $231.55   $231.60  
  7 purchase totals = $950.77       $1,026.0611   $1,026.06   $1,026.00   $1,026.00