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 $222.50   10.445%   $245.7401   $245.74   $245.75   $245.70  
  Purchase #2 $63.69   4.185%   $66.3554   $66.36   $66.35   $66.40  
  Purchase #3 $34.32   7.786%   $36.9922   $36.99   $37.00   $37.00  
  Purchase #4 $201.98   3.360%   $208.7665   $208.77   $208.75   $208.80  
  Purchase #5 $77.36   9.112%   $84.409   $84.41   $84.40   $84.40  
  Purchase #6 $140.88   13.240%   $159.5325   $159.53   $159.55   $159.50  
  Purchase #7 $234.25   5.173%   $246.3678   $246.37   $246.35   $246.40  
  7 purchase totals = $974.98       $1,048.1635   $1,048.17   $1,048.15   $1,048.20