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 $132.31   5.518%   $139.6109   $139.61   $139.60   $139.60  
  Purchase #2 $132.79   11.157%   $147.6054   $147.61   $147.60   $147.60  
  Purchase #3 $208.71   6.315%   $221.89   $221.89   $221.90   $221.90  
  Purchase #4 $138.55   13.515%   $157.275   $157.28   $157.30   $157.30  
  Purchase #5 $31.49   11.147%   $35.0002   $35.00   $35.00   $35.00  
  Purchase #6 $34.45   3.367%   $35.6099   $35.61   $35.60   $35.60  
  Purchase #7 $18.25   10.608%   $20.186   $20.19   $20.20   $20.20  
  7 purchase totals = $696.55       $757.1774   $757.19   $757.20   $757.20