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 $58.62   8.855%   $63.8108   $63.81   $63.80   $63.80  
  Purchase #2 $73.74   3.367%   $76.2228   $76.22   $76.20   $76.20  
  Purchase #3 $207.28   8.864%   $225.6533   $225.65   $225.65   $225.70  
  Purchase #4 $225.98   7.410%   $242.7251   $242.73   $242.75   $242.70  
  Purchase #5 $232.59   10.389%   $256.7538   $256.75   $256.75   $256.80  
  Purchase #6 $93.69   6.411%   $99.6965   $99.70   $99.70   $99.70  
  Purchase #7 $136.99   5.310%   $144.2642   $144.26   $144.25   $144.30  
  7 purchase totals = $1,028.89       $1,109.1265   $1,109.12   $1,109.10   $1,109.20