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 $103.86   12.221%   $116.5527   $116.55   $116.55   $116.60  
  Purchase #2 $239.26   11.744%   $267.3587   $267.36   $267.35   $267.40  
  Purchase #3 $107.74   13.564%   $122.3539   $122.35   $122.35   $122.40  
  Purchase #4 $195.76   10.477%   $216.2698   $216.27   $216.25   $216.30  
  Purchase #5 $220.47   5.475%   $232.5407   $232.54   $232.55   $232.50  
  Purchase #6 $40.99   8.676%   $44.5463   $44.55   $44.55   $44.50  
  Purchase #7 $235.97   5.502%   $248.9531   $248.95   $248.95   $249.00  
  7 purchase totals = $1,144.05       $1,248.5752   $1,248.57   $1,248.55   $1,248.70