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 $247.81   8.522%   $268.9284   $268.93   $268.95   $268.90  
  Purchase #2 $157.87   10.819%   $174.95   $174.95   $174.95   $175.00  
  Purchase #3 $85.75   12.870%   $96.786   $96.79   $96.80   $96.80  
  Purchase #4 $196.47   7.413%   $211.0343   $211.03   $211.05   $211.00  
  Purchase #5 $144.64   8.116%   $156.379   $156.38   $156.40   $156.40  
  Purchase #6 $222.86   12.672%   $251.1008   $251.10   $251.10   $251.10  
  Purchase #7 $8.66   11.745%   $9.6771   $9.68   $9.70   $9.70  
  7 purchase totals = $1,064.06       $1,168.8556   $1,168.86   $1,168.95   $1,168.90