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 $155.67   3.617%   $161.3006   $161.30   $161.30   $161.30  
  Purchase #2 $221.37   10.524%   $244.667   $244.67   $244.65   $244.70  
  Purchase #3 $133.79   6.793%   $142.8784   $142.88   $142.90   $142.90  
  Purchase #4 $161.48   8.366%   $174.9894   $174.99   $175.00   $175.00  
  Purchase #5 $246.27   12.166%   $276.2312   $276.23   $276.25   $276.20  
  Purchase #6 $119.36   10.103%   $131.4189   $131.42   $131.40   $131.40  
  Purchase #7 $80.66   10.600%   $89.21   $89.21   $89.20   $89.20  
  7 purchase totals = $1,118.60       $1,220.6955   $1,220.70   $1,220.70   $1,220.70