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 $193.78   6.152%   $205.7013   $205.70   $205.70   $205.70  
  Purchase #2 $106.85   8.658%   $116.1011   $116.10   $116.10   $116.10  
  Purchase #3 $233.71   4.791%   $244.907   $244.91   $244.90   $244.90  
  Purchase #4 $41.82   12.412%   $47.0107   $47.01   $47.00   $47.00  
  Purchase #5 $78.99   7.693%   $85.0667   $85.07   $85.05   $85.10  
  Purchase #6 $8.32   10.612%   $9.2029   $9.20   $9.20   $9.20  
  Purchase #7 $151.64   9.631%   $166.2444   $166.24   $166.25   $166.20  
  7 purchase totals = $815.11       $874.2341   $874.23   $874.20   $874.20