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 $130.94   7.651%   $140.9582   $140.96   $140.95   $141.00  
  Purchase #2 $181.50   13.687%   $206.3419   $206.34   $206.35   $206.30  
  Purchase #3 $216.71   11.849%   $242.388   $242.39   $242.40   $242.40  
  Purchase #4 $191.96   13.228%   $217.3525   $217.35   $217.35   $217.40  
  Purchase #5 $60.26   9.245%   $65.831   $65.83   $65.85   $65.80  
  Purchase #6 $242.86   10.874%   $269.2686   $269.27   $269.25   $269.30  
  Purchase #7 $68.49   5.845%   $72.4932   $72.49   $72.50   $72.50  
  7 purchase totals = $1,092.72       $1,214.6334   $1,214.63   $1,214.65   $1,214.70