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	$46.86	7.200%	$50.2339	$50.23	$50.25	$50.20
Purchase #2	$215.89	5.681%	$228.1547	$228.15	$228.15	$228.20
Purchase #3	$158.79	13.200%	$179.7503	$179.75	$179.75	$179.80
Purchase #4	$95.26	10.540%	$105.3004	$105.30	$105.30	$105.30
Purchase #5	$187.78	13.595%	$213.3087	$213.31	$213.30	$213.30
Purchase #6	$235.27	4.388%	$245.5936	$245.59	$245.60	$245.60
Purchase #7	$222.60	4.850%	$233.3961	$233.40	$233.40	$233.40
7 purchase totals =	$1,162.45		$1,255.7377	$1,255.73	$1,255.75	$1,255.80