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 $89.47   7.410%   $96.0997   $96.10   $96.10   $96.10  
  Purchase #2 $124.34   10.717%   $137.6655   $137.67   $137.65   $137.70  
  Purchase #3 $192.79   13.590%   $218.9902   $218.99   $219.00   $219.00  
  Purchase #4 $149.35   5.733%   $157.9122   $157.91   $157.90   $157.90  
  Purchase #5 $206.80   13.241%   $234.1824   $234.18   $234.20   $234.20  
  Purchase #6 $242.75   7.704%   $261.4515   $261.45   $261.45   $261.50  
  Purchase #7 $225.96   8.642%   $245.4875   $245.49   $245.50   $245.50  
  7 purchase totals = $1,231.46       $1,351.7890   $1,351.79   $1,351.80   $1,351.90