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 $222.29   3.492%   $230.0524   $230.05   $230.05   $230.10  
  Purchase #2 $5.74   10.307%   $6.3316   $6.33   $6.35   $6.30  
  Purchase #3 $151.86   7.333%   $162.9959   $163.00   $163.00   $163.00  
  Purchase #4 $60.40   12.287%   $67.8213   $67.82   $67.80   $67.80  
  Purchase #5 $216.82   10.653%   $239.9178   $239.92   $239.90   $239.90  
  Purchase #6 $86.62   10.815%   $95.988   $95.99   $96.00   $96.00  
  Purchase #7 $57.58   13.358%   $65.2715   $65.27   $65.25   $65.30  
  7 purchase totals = $801.31       $868.3785   $868.38   $868.35   $868.40