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	$59.90	4.399%	$62.535	$62.54	$62.55	$62.50
Purchase #2	$101.89	8.508%	$110.5588	$110.56	$110.55	$110.60
Purchase #3	$37.37	4.122%	$38.9104	$38.91	$38.90	$38.90
Purchase #4	$191.46	12.583%	$215.5514	$215.55	$215.55	$215.60
Purchase #5	$175.51	3.497%	$181.6476	$181.65	$181.65	$181.60
Purchase #6	$143.91	11.726%	$160.7849	$160.78	$160.80	$160.80
Purchase #7	$132.72	5.774%	$140.3833	$140.38	$140.40	$140.40
7 purchase totals =	$842.76		$910.3714	$910.37	$910.40	$910.40