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 $169.72   10.185%   $187.006   $187.01   $187.00   $187.00  
  Purchase #2 $226.60   12.821%   $255.6524   $255.65   $255.65   $255.70  
  Purchase #3 $86.71   13.380%   $98.3118   $98.31   $98.30   $98.30  
  Purchase #4 $220.77   12.339%   $248.0108   $248.01   $248.00   $248.00  
  Purchase #5 $193.68   7.863%   $208.9091   $208.91   $208.90   $208.90  
  Purchase #6 $225.96   7.433%   $242.7556   $242.76   $242.75   $242.80  
  Purchase #7 $23.96   6.821%   $25.5943   $25.59   $25.60   $25.60  
  7 purchase totals = $1,147.40       $1,266.2400   $1,266.24   $1,266.20   $1,266.30