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 $247.97   11.396%   $276.2287   $276.23   $276.25   $276.20  
  Purchase #2 $177.88   8.651%   $193.2684   $193.27   $193.25   $193.30  
  Purchase #3 $165.98   11.430%   $184.9515   $184.95   $184.95   $185.00  
  Purchase #4 $156.55   12.559%   $176.2111   $176.21   $176.20   $176.20  
  Purchase #5 $153.38   8.725%   $166.7624   $166.76   $166.75   $166.80  
  Purchase #6 $158.27   12.690%   $178.3545   $178.35   $178.35   $178.40  
  Purchase #7 $221.90   13.694%   $252.287   $252.29   $252.30   $252.30  
  7 purchase totals = $1,281.93       $1,428.0636   $1,428.06   $1,428.05   $1,428.20