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 $58.48   4.549%   $61.1403   $61.14   $61.15   $61.10  
  Purchase #2 $14.83   7.628%   $15.9612   $15.96   $15.95   $16.00  
  Purchase #3 $70.99   3.248%   $73.2958   $73.30   $73.30   $73.30  
  Purchase #4 $65.92   4.701%   $69.0189   $69.02   $69.00   $69.00  
  Purchase #5 $247.91   12.724%   $279.4541   $279.45   $279.45   $279.50  
  Purchase #6 $183.46   7.684%   $197.5571   $197.56   $197.55   $197.60  
  Purchase #7 $240.90   5.811%   $254.8987   $254.90   $254.90   $254.90  
  7 purchase totals = $882.49       $951.3261   $951.33   $951.30   $951.40