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 $24.62   8.112%   $26.6172   $26.62   $26.60   $26.60  
  Purchase #2 $198.56   10.374%   $219.1586   $219.16   $219.15   $219.20  
  Purchase #3 $79.80   9.747%   $87.5781   $87.58   $87.60   $87.60  
  Purchase #4 $111.44   6.705%   $118.9121   $118.91   $118.90   $118.90  
  Purchase #5 $154.40   5.788%   $163.3367   $163.34   $163.35   $163.30  
  Purchase #6 $50.25   5.661%   $53.0947   $53.09   $53.10   $53.10  
  Purchase #7 $145.46   3.864%   $151.0806   $151.08   $151.10   $151.10  
  7 purchase totals = $764.53       $819.7780   $819.78   $819.80   $819.80