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	$28.28	7.116%	$30.2924	$30.29	$30.30	$30.30
Purchase #2	$70.57	3.395%	$72.9659	$72.97	$72.95	$73.00
Purchase #3	$194.62	7.614%	$209.4384	$209.44	$209.45	$209.40
Purchase #4	$130.82	13.682%	$148.7188	$148.72	$148.70	$148.70
Purchase #5	$65.79	10.583%	$72.7526	$72.75	$72.75	$72.80
Purchase #6	$39.69	13.391%	$45.0049	$45.00	$45.00	$45.00
Purchase #7	$206.27	9.293%	$225.4387	$225.44	$225.45	$225.40
7 purchase totals =	$736.04		$804.6117	$804.61	$804.60	$804.60