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 $207.42   7.632%   $223.2503   $223.25   $223.25   $223.30  
  Purchase #2 $103.83   11.505%   $115.7756   $115.78   $115.80   $115.80  
  Purchase #3 $234.81   5.187%   $246.9896   $246.99   $247.00   $247.00  
  Purchase #4 $122.58   8.557%   $133.0692   $133.07   $133.05   $133.10  
  Purchase #5 $12.66   9.405%   $13.8507   $13.85   $13.85   $13.90  
  Purchase #6 $246.38   11.469%   $274.6373   $274.64   $274.65   $274.60  
  Purchase #7 $8.67   5.846%   $9.1768   $9.18   $9.20   $9.20  
  7 purchase totals = $936.35       $1,016.7495   $1,016.76   $1,016.80   $1,016.90