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 $176.51   5.393%   $186.0292   $186.03   $186.05   $186.00  
  Purchase #2 $248.98   9.215%   $271.9235   $271.92   $271.90   $271.90  
  Purchase #3 $235.96   12.844%   $266.2667   $266.27   $266.25   $266.30  
  Purchase #4 $129.32   10.827%   $143.3215   $143.32   $143.30   $143.30  
  Purchase #5 $102.25   7.570%   $109.9903   $109.99   $110.00   $110.00  
  Purchase #6 $89.58   3.534%   $92.7458   $92.75   $92.75   $92.70  
  Purchase #7 $8.75   3.527%   $9.0586   $9.06   $9.05   $9.10  
  7 purchase totals = $991.35       $1,079.3356   $1,079.34   $1,079.30   $1,079.30