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 $222.95   7.501%   $239.6735   $239.67   $239.65   $239.70  
  Purchase #2 $124.47   6.487%   $132.5444   $132.54   $132.55   $132.50  
  Purchase #3 $217.70   6.503%   $231.857   $231.86   $231.85   $231.90  
  Purchase #4 $76.26   12.719%   $85.9595   $85.96   $85.95   $86.00  
  Purchase #5 $229.30   6.643%   $244.5324   $244.53   $244.55   $244.50  
  Purchase #6 $19.31   10.754%   $21.3866   $21.39   $21.40   $21.40  
  Purchase #7 $172.89   4.334%   $180.3831   $180.38   $180.40   $180.40  
  7 purchase totals = $1,062.88       $1,136.3365   $1,136.33   $1,136.35   $1,136.40