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	$162.87	5.117%	$171.2041	$171.20	$171.20	$171.20
Purchase #2	$159.55	10.644%	$176.5325	$176.53	$176.55	$176.50
Purchase #3	$232.28	9.150%	$253.5336	$253.53	$253.55	$253.50
Purchase #4	$107.39	4.162%	$111.8596	$111.86	$111.85	$111.90
Purchase #5	$33.80	4.607%	$35.3572	$35.36	$35.35	$35.40
Purchase #6	$85.86	5.277%	$90.3908	$90.39	$90.40	$90.40
Purchase #7	$222.69	9.755%	$244.4134	$244.41	$244.40	$244.40
7 purchase totals =	$1,004.44		$1,083.2912	$1,083.28	$1,083.30	$1,083.30