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 $92.64   9.182%   $101.1462   $101.15   $101.15   $101.10  
  Purchase #2 $229.90   6.726%   $245.3631   $245.36   $245.35   $245.40  
  Purchase #3 $32.47   5.242%   $34.1721   $34.17   $34.15   $34.20  
  Purchase #4 $166.31   4.433%   $173.6825   $173.68   $173.70   $173.70  
  Purchase #5 $18.28   9.149%   $19.9524   $19.95   $19.95   $20.00  
  Purchase #6 $170.72   8.526%   $185.2756   $185.28   $185.30   $185.30  
  Purchase #7 $35.94   5.670%   $37.9778   $37.98   $38.00   $38.00  
  7 purchase totals = $746.26       $797.5697   $797.57   $797.60   $797.70