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 $203.45   3.804%   $211.1892   $211.19   $211.20   $211.20  
  Purchase #2 $168.87   13.864%   $192.2821   $192.28   $192.30   $192.30  
  Purchase #3 $63.74   3.398%   $65.9059   $65.91   $65.90   $65.90  
  Purchase #4 $164.99   5.116%   $173.4309   $173.43   $173.45   $173.40  
  Purchase #5 $144.38   7.562%   $155.298   $155.30   $155.30   $155.30  
  Purchase #6 $45.76   8.702%   $49.742   $49.74   $49.75   $49.70  
  Purchase #7 $62.78   12.354%   $70.5358   $70.54   $70.55   $70.50  
  7 purchase totals = $853.97       $918.3839   $918.39   $918.45   $918.30