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	$52.40	7.454%	$56.3059	$56.31	$56.30	$56.30
Purchase #2	$234.57	13.231%	$265.606	$265.61	$265.60	$265.60
Purchase #3	$173.68	6.651%	$185.2315	$185.23	$185.25	$185.20
Purchase #4	$102.61	8.637%	$111.4724	$111.47	$111.45	$111.50
Purchase #5	$25.27	6.397%	$26.8865	$26.89	$26.90	$26.90
Purchase #6	$243.86	10.458%	$269.3629	$269.36	$269.35	$269.40
Purchase #7	$97.85	7.635%	$105.3208	$105.32	$105.30	$105.30
7 purchase totals =	$930.24		$1,020.1860	$1,020.19	$1,020.15	$1,020.20