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 $38.84   12.215%   $43.5843   $43.58   $43.60   $43.60  
  Purchase #2 $157.97   5.485%   $166.6347   $166.63   $166.65   $166.60  
  Purchase #3 $145.92   8.461%   $158.2663   $158.27   $158.25   $158.30  
  Purchase #4 $102.44   11.838%   $114.5668   $114.57   $114.55   $114.60  
  Purchase #5 $69.77   6.776%   $74.4976   $74.50   $74.50   $74.50  
  Purchase #6 $190.85   4.416%   $199.2779   $199.28   $199.30   $199.30  
  Purchase #7 $113.31   3.514%   $117.2917   $117.29   $117.30   $117.30  
  7 purchase totals = $819.10       $874.1193   $874.12   $874.15   $874.20