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 $112.33   10.153%   $123.7349   $123.73   $123.75   $123.70  
  Purchase #2 $79.80   4.693%   $83.545   $83.55   $83.55   $83.50  
  Purchase #3 $78.88   7.180%   $84.5436   $84.54   $84.55   $84.50  
  Purchase #4 $74.84   12.469%   $84.1718   $84.17   $84.15   $84.20  
  Purchase #5 $243.61   4.873%   $255.4811   $255.48   $255.50   $255.50  
  Purchase #6 $236.64   11.503%   $263.8607   $263.86   $263.85   $263.90  
  Purchase #7 $167.81   3.111%   $173.0306   $173.03   $173.05   $173.00  
  7 purchase totals = $993.91       $1,068.3677   $1,068.36   $1,068.40   $1,068.30