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 $16.62   7.865%   $17.9272   $17.93   $17.95   $17.90  
  Purchase #2 $235.82   13.487%   $267.625   $267.63   $267.65   $267.60  
  Purchase #3 $142.37   7.402%   $152.9082   $152.91   $152.90   $152.90  
  Purchase #4 $220.69   12.579%   $248.4506   $248.45   $248.45   $248.50  
  Purchase #5 $84.65   4.198%   $88.2036   $88.20   $88.20   $88.20  
  Purchase #6 $46.38   10.516%   $51.2573   $51.26   $51.25   $51.30  
  Purchase #7 $80.79   8.496%   $87.6539   $87.65   $87.65   $87.70  
  7 purchase totals = $827.32       $914.0258   $914.03   $914.05   $914.10