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 $32.48   9.553%   $35.5828   $35.58   $35.60   $35.60  
  Purchase #2 $63.41   10.191%   $69.8721   $69.87   $69.85   $69.90  
  Purchase #3 $107.87   7.528%   $115.9905   $115.99   $116.00   $116.00  
  Purchase #4 $175.60   3.422%   $181.609   $181.61   $181.60   $181.60  
  Purchase #5 $164.32   6.552%   $175.0862   $175.09   $175.10   $175.10  
  Purchase #6 $176.80   4.191%   $184.2097   $184.21   $184.20   $184.20  
  Purchase #7 $220.66   6.521%   $235.0492   $235.05   $235.05   $235.00  
  7 purchase totals = $941.14       $997.3995   $997.40   $997.40   $997.40