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 $40.99   8.638%   $44.5307   $44.53   $44.55   $44.50  
  Purchase #2 $68.61   3.495%   $71.0079   $71.01   $71.00   $71.00  
  Purchase #3 $76.28   12.663%   $85.9393   $85.94   $85.95   $85.90  
  Purchase #4 $249.77   9.549%   $273.6205   $273.62   $273.60   $273.60  
  Purchase #5 $196.94   3.157%   $203.1574   $203.16   $203.15   $203.20  
  Purchase #6 $233.62   12.844%   $263.6262   $263.63   $263.65   $263.60  
  Purchase #7 $13.29   5.824%   $14.064   $14.06   $14.05   $14.10  
  7 purchase totals = $879.50       $955.9460   $955.95   $955.95   $955.90