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	$88.84	13.170%	$100.5402	$100.54	$100.55	$100.50
Purchase #2	$52.65	5.725%	$55.6642	$55.66	$55.65	$55.70
Purchase #3	$26.96	7.796%	$29.0618	$29.06	$29.05	$29.10
Purchase #4	$200.54	11.135%	$222.8701	$222.87	$222.85	$222.90
Purchase #5	$103.25	6.342%	$109.7981	$109.80	$109.80	$109.80
Purchase #6	$145.36	11.549%	$162.1476	$162.15	$162.15	$162.10
Purchase #7	$190.89	12.228%	$214.232	$214.23	$214.25	$214.20
7 purchase totals =	$808.49		$894.3140	$894.31	$894.30	$894.30