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 $95.99   5.697%   $101.4586   $101.46   $101.45   $101.50  
  Purchase #2 $25.63   12.262%   $28.7728   $28.77   $28.75   $28.80  
  Purchase #3 $120.90   3.557%   $125.2004   $125.20   $125.20   $125.20  
  Purchase #4 $215.54   12.788%   $243.1033   $243.10   $243.10   $243.10  
  Purchase #5 $212.57   12.733%   $239.6365   $239.64   $239.65   $239.60  
  Purchase #6 $218.49   13.735%   $248.4996   $248.50   $248.50   $248.50  
  Purchase #7 $65.71   13.520%   $74.594   $74.59   $74.60   $74.60  
  7 purchase totals = $954.83       $1,061.2652   $1,061.26   $1,061.25   $1,061.30