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 $38.95   11.164%   $43.2984   $43.30   $43.30   $43.30  
  Purchase #2 $232.46   12.575%   $261.6918   $261.69   $261.70   $261.70  
  Purchase #3 $190.50   13.473%   $216.1661   $216.17   $216.15   $216.20  
  Purchase #4 $63.49   5.719%   $67.121   $67.12   $67.10   $67.10  
  Purchase #5 $49.54   4.597%   $51.8174   $51.82   $51.80   $51.80  
  Purchase #6 $208.65   10.250%   $230.0366   $230.04   $230.05   $230.00  
  Purchase #7 $150.98   5.643%   $159.4998   $159.50   $159.50   $159.50  
  7 purchase totals = $934.57       $1,029.6311   $1,029.64   $1,029.60   $1,029.60