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 $163.39   12.177%   $183.286   $183.29   $183.30   $183.30  
  Purchase #2 $71.35   3.186%   $73.6232   $73.62   $73.60   $73.60  
  Purchase #3 $248.82   13.303%   $281.9205   $281.92   $281.90   $281.90  
  Purchase #4 $201.62   5.258%   $212.2212   $212.22   $212.20   $212.20  
  Purchase #5 $8.83   13.659%   $10.0361   $10.04   $10.05   $10.00  
  Purchase #6 $165.58   12.132%   $185.6682   $185.67   $185.65   $185.70  
  Purchase #7 $43.31   10.546%   $47.8775   $47.88   $47.90   $47.90  
  7 purchase totals = $902.90       $994.6327   $994.64   $994.60   $994.60