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 $214.38   13.233%   $242.7489   $242.75   $242.75   $242.70  
  Purchase #2 $122.68   6.820%   $131.0468   $131.05   $131.05   $131.00  
  Purchase #3 $159.25   10.732%   $176.3407   $176.34   $176.35   $176.30  
  Purchase #4 $23.65   4.869%   $24.8015   $24.80   $24.80   $24.80  
  Purchase #5 $11.80   4.860%   $12.3735   $12.37   $12.35   $12.40  
  Purchase #6 $114.80   6.321%   $122.0565   $122.06   $122.05   $122.10  
  Purchase #7 $208.58   11.667%   $232.915   $232.92   $232.90   $232.90  
  7 purchase totals = $855.14       $942.2829   $942.29   $942.25   $942.20