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 $68.62   11.767%   $76.6945   $76.69   $76.70   $76.70  
  Purchase #2 $108.35   7.670%   $116.6604   $116.66   $116.65   $116.70  
  Purchase #3 $35.32   12.318%   $39.6707   $39.67   $39.65   $39.70  
  Purchase #4 $86.58   3.636%   $89.728   $89.73   $89.75   $89.70  
  Purchase #5 $134.60   6.728%   $143.6559   $143.66   $143.65   $143.70  
  Purchase #6 $212.58   6.345%   $226.0682   $226.07   $226.05   $226.10  
  Purchase #7 $151.71   11.676%   $169.4237   $169.42   $169.40   $169.40  
  7 purchase totals = $797.76       $861.9014   $861.90   $861.85   $862.00