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 $185.87   13.757%   $211.4401   $211.44   $211.45   $211.40  
  Purchase #2 $35.27   8.161%   $38.1484   $38.15   $38.15   $38.10  
  Purchase #3 $155.63   13.433%   $176.5358   $176.54   $176.55   $176.50  
  Purchase #4 $120.93   13.679%   $137.472   $137.47   $137.45   $137.50  
  Purchase #5 $26.90   7.179%   $28.8312   $28.83   $28.85   $28.80  
  Purchase #6 $124.58   12.585%   $140.2584   $140.26   $140.25   $140.30  
  Purchase #7 $31.26   12.732%   $35.24   $35.24   $35.25   $35.20  
  7 purchase totals = $680.44       $767.9259   $767.93   $767.95   $767.80