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 $169.33   8.827%   $184.2768   $184.28   $184.30   $184.30  
  Purchase #2 $156.68   6.520%   $166.8955   $166.90   $166.90   $166.90  
  Purchase #3 $16.37   4.723%   $17.1432   $17.14   $17.15   $17.10  
  Purchase #4 $149.80   11.439%   $166.9356   $166.94   $166.95   $166.90  
  Purchase #5 $189.70   8.715%   $206.2324   $206.23   $206.25   $206.20  
  Purchase #6 $165.45   11.385%   $184.2865   $184.29   $184.30   $184.30  
  Purchase #7 $250.90   6.382%   $266.9124   $266.91   $266.90   $266.90  
  7 purchase totals = $1,098.23       $1,192.6824   $1,192.69   $1,192.75   $1,192.60