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	$80.32	10.452%	$88.715	$88.72	$88.70	$88.70
Purchase #2	$249.89	8.499%	$271.1282	$271.13	$271.15	$271.10
Purchase #3	$78.99	3.174%	$81.4971	$81.50	$81.50	$81.50
Purchase #4	$163.32	6.852%	$174.5107	$174.51	$174.50	$174.50
Purchase #5	$106.51	3.136%	$109.8502	$109.85	$109.85	$109.90
Purchase #6	$194.56	5.618%	$205.4904	$205.49	$205.50	$205.50
Purchase #7	$85.33	4.442%	$89.1204	$89.12	$89.10	$89.10
7 purchase totals =	$958.92		$1,020.3120	$1,020.32	$1,020.30	$1,020.30