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	$165.72	12.185%	$185.913	$185.91	$185.90	$185.90
Purchase #2	$247.47	5.536%	$261.1699	$261.17	$261.15	$261.20
Purchase #3	$109.40	4.795%	$114.6457	$114.65	$114.65	$114.60
Purchase #4	$65.73	8.372%	$71.2329	$71.23	$71.25	$71.20
Purchase #5	$53.79	13.594%	$61.1022	$61.10	$61.10	$61.10
Purchase #6	$91.89	7.250%	$98.552	$98.55	$98.55	$98.60
Purchase #7	$29.50	7.622%	$31.7485	$31.75	$31.75	$31.70
7 purchase totals =	$763.50		$824.3642	$824.36	$824.35	$824.30