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 $69.79   10.206%   $76.9128   $76.91   $76.90   $76.90  
  Purchase #2 $174.50   7.696%   $187.9295   $187.93   $187.95   $187.90  
  Purchase #3 $130.53   3.422%   $134.9967   $135.00   $135.00   $135.00  
  Purchase #4 $39.39   5.772%   $41.6636   $41.66   $41.65   $41.70  
  Purchase #5 $189.71   13.294%   $214.93   $214.93   $214.95   $214.90  
  Purchase #6 $46.86   6.758%   $50.0268   $50.03   $50.05   $50.00  
  Purchase #7 $76.26   3.368%   $78.8284   $78.83   $78.85   $78.80  
  7 purchase totals = $727.04       $785.2878   $785.29   $785.35   $785.20