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	$85.87	3.350%	$88.7466	$88.75	$88.75	$88.70
Purchase #2	$148.40	8.111%	$160.4367	$160.44	$160.45	$160.40
Purchase #3	$122.94	6.650%	$131.1155	$131.12	$131.10	$131.10
Purchase #4	$69.48	13.512%	$78.8681	$78.87	$78.85	$78.90
Purchase #5	$214.54	7.132%	$229.841	$229.84	$229.85	$229.80
Purchase #6	$79.63	12.251%	$89.3855	$89.39	$89.40	$89.40
Purchase #7	$17.36	10.868%	$19.2467	$19.25	$19.25	$19.20
7 purchase totals =	$738.22		$797.6401	$797.66	$797.65	$797.50