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 $23.44   12.247%   $26.3107   $26.31   $26.30   $26.30  
  Purchase #2 $182.52   5.669%   $192.8671   $192.87   $192.85   $192.90  
  Purchase #3 $209.29   7.278%   $224.5221   $224.52   $224.50   $224.50  
  Purchase #4 $163.62   3.391%   $169.1684   $169.17   $169.15   $169.20  
  Purchase #5 $232.43   12.726%   $262.009   $262.01   $262.00   $262.00  
  Purchase #6 $34.64   3.174%   $35.7395   $35.74   $35.75   $35.70  
  Purchase #7 $96.98   12.725%   $109.3207   $109.32   $109.30   $109.30  
  7 purchase totals = $942.92       $1,019.9375   $1,019.94   $1,019.85   $1,019.90