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 $76.74   12.731%   $86.5098   $86.51   $86.50   $86.50  
  Purchase #2 $126.37   8.612%   $137.253   $137.25   $137.25   $137.30  
  Purchase #3 $27.88   4.250%   $29.0649   $29.06   $29.05   $29.10  
  Purchase #4 $233.78   7.704%   $251.7904   $251.79   $251.80   $251.80  
  Purchase #5 $35.90   8.154%   $38.8273   $38.83   $38.85   $38.80  
  Purchase #6 $101.69   10.166%   $112.0278   $112.03   $112.05   $112.00  
  Purchase #7 $145.44   4.353%   $151.771   $151.77   $151.75   $151.80  
  7 purchase totals = $747.80       $807.2442   $807.24   $807.25   $807.30