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 $161.73   10.428%   $178.5952   $178.60   $178.60   $178.60  
  Purchase #2 $67.59   8.377%   $73.252   $73.25   $73.25   $73.30  
  Purchase #3 $188.42   13.551%   $213.9528   $213.95   $213.95   $214.00  
  Purchase #4 $182.69   6.401%   $194.384   $194.38   $194.40   $194.40  
  Purchase #5 $145.74   6.186%   $154.7555   $154.76   $154.75   $154.80  
  Purchase #6 $210.81   11.366%   $234.7707   $234.77   $234.75   $234.80  
  Purchase #7 $172.44   12.319%   $193.6829   $193.68   $193.70   $193.70  
  7 purchase totals = $1,129.42       $1,243.3931   $1,243.39   $1,243.40   $1,243.60