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 $187.40   9.554%   $205.3042   $205.30   $205.30   $205.30  
  Purchase #2 $104.87   13.125%   $118.6342   $118.63   $118.65   $118.60  
  Purchase #3 $157.64   3.851%   $163.7107   $163.71   $163.70   $163.70  
  Purchase #4 $55.71   11.165%   $61.93   $61.93   $61.95   $61.90  
  Purchase #5 $154.29   7.594%   $166.0068   $166.01   $166.00   $166.00  
  Purchase #6 $157.95   7.113%   $169.185   $169.19   $169.20   $169.20  
  Purchase #7 $11.77   4.164%   $12.2601   $12.26   $12.25   $12.30  
  7 purchase totals = $829.63       $897.0310   $897.03   $897.05   $897.00