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 $191.64   6.341%   $203.7919   $203.79   $203.80   $203.80  
  Purchase #2 $167.25   10.674%   $185.1023   $185.10   $185.10   $185.10  
  Purchase #3 $134.38   11.137%   $149.3459   $149.35   $149.35   $149.30  
  Purchase #4 $250.28   10.151%   $275.6859   $275.69   $275.70   $275.70  
  Purchase #5 $141.95   7.714%   $152.9   $152.90   $152.90   $152.90  
  Purchase #6 $233.44   13.845%   $265.7598   $265.76   $265.75   $265.80  
  Purchase #7 $179.36   7.420%   $192.6685   $192.67   $192.65   $192.70  
  7 purchase totals = $1,298.30       $1,425.2543   $1,425.26   $1,425.25   $1,425.30