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 $62.33   10.473%   $68.8578   $68.86   $68.85   $68.90  
  Purchase #2 $114.66   3.170%   $118.2947   $118.29   $118.30   $118.30  
  Purchase #3 $74.52   9.500%   $81.5994   $81.60   $81.60   $81.60  
  Purchase #4 $155.59   8.569%   $168.9225   $168.92   $168.90   $168.90  
  Purchase #5 $111.81   10.178%   $123.19   $123.19   $123.20   $123.20  
  Purchase #6 $27.43   12.501%   $30.859   $30.86   $30.85   $30.90  
  Purchase #7 $79.89   11.354%   $88.9607   $88.96   $88.95   $89.00  
  7 purchase totals = $626.23       $680.6841   $680.68   $680.65   $680.80