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 $64.83   6.255%   $68.8851   $68.89   $68.90   $68.90  
  Purchase #2 $228.55   7.309%   $245.2547   $245.25   $245.25   $245.30  
  Purchase #3 $106.88   7.560%   $114.9601   $114.96   $114.95   $115.00  
  Purchase #4 $59.91   7.442%   $64.3685   $64.37   $64.35   $64.40  
  Purchase #5 $27.65   6.697%   $29.5017   $29.50   $29.50   $29.50  
  Purchase #6 $232.76   7.511%   $250.2426   $250.24   $250.25   $250.20  
  Purchase #7 $14.49   3.385%   $14.9805   $14.98   $15.00   $15.00  
  7 purchase totals = $735.07       $788.1932   $788.19   $788.20   $788.30