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 $118.97   6.366%   $126.5436   $126.54   $126.55   $126.50  
  Purchase #2 $76.66   6.461%   $81.613   $81.61   $81.60   $81.60  
  Purchase #3 $195.99   8.512%   $212.6727   $212.67   $212.65   $212.70  
  Purchase #4 $206.31   4.824%   $216.2624   $216.26   $216.25   $216.30  
  Purchase #5 $179.91   3.430%   $186.0809   $186.08   $186.10   $186.10  
  Purchase #6 $226.41   11.802%   $253.1309   $253.13   $253.15   $253.10  
  Purchase #7 $223.75   10.604%   $247.4765   $247.48   $247.50   $247.50  
  7 purchase totals = $1,228.00       $1,323.7800   $1,323.77   $1,323.80   $1,323.80