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 $227.98   11.268%   $253.6688   $253.67   $253.65   $253.70  
  Purchase #2 $96.49   9.725%   $105.8737   $105.87   $105.85   $105.90  
  Purchase #3 $30.79   3.263%   $31.7947   $31.79   $31.80   $31.80  
  Purchase #4 $208.81   3.821%   $216.7886   $216.79   $216.80   $216.80  
  Purchase #5 $152.69   7.517%   $164.1677   $164.17   $164.15   $164.20  
  Purchase #6 $104.38   11.237%   $116.1092   $116.11   $116.10   $116.10  
  Purchase #7 $114.28   9.865%   $125.5537   $125.55   $125.55   $125.60  
  7 purchase totals = $935.42       $1,013.9564   $1,013.95   $1,013.90   $1,014.10