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	$47.60	10.307%	$52.5061	$52.51	$52.50	$52.50
Purchase #2	$43.92	6.487%	$46.7691	$46.77	$46.75	$46.80
Purchase #3	$105.98	7.807%	$114.2539	$114.25	$114.25	$114.30
Purchase #4	$223.28	13.560%	$253.5568	$253.56	$253.55	$253.60
Purchase #5	$134.41	6.599%	$143.2797	$143.28	$143.30	$143.30
Purchase #6	$144.36	5.577%	$152.411	$152.41	$152.40	$152.40
Purchase #7	$221.45	8.485%	$240.24	$240.24	$240.25	$240.20
7 purchase totals =	$921.00		$1,003.0166	$1,003.02	$1,003.00	$1,003.10