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 $171.76   8.326%   $186.0607   $186.06   $186.05   $186.10  
  Purchase #2 $29.33   13.686%   $33.3441   $33.34   $33.35   $33.30  
  Purchase #3 $215.44   5.209%   $226.6623   $226.66   $226.65   $226.70  
  Purchase #4 $220.38   6.784%   $235.3306   $235.33   $235.35   $235.30  
  Purchase #5 $204.25   9.622%   $223.9029   $223.90   $223.90   $223.90  
  Purchase #6 $79.40   4.614%   $83.0635   $83.06   $83.05   $83.10  
  Purchase #7 $228.29   8.202%   $247.0143   $247.01   $247.00   $247.00  
  7 purchase totals = $1,148.85       $1,235.3784   $1,235.36   $1,235.35   $1,235.40