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	$159.47	7.416%	$171.2963	$171.30	$171.30	$171.30
Purchase #2	$105.51	8.327%	$114.2958	$114.30	$114.30	$114.30
Purchase #3	$186.47	12.482%	$209.7452	$209.75	$209.75	$209.70
Purchase #4	$153.44	8.342%	$166.24	$166.24	$166.25	$166.20
Purchase #5	$36.29	3.777%	$37.6607	$37.66	$37.65	$37.70
Purchase #6	$215.49	3.298%	$222.5969	$222.60	$222.60	$222.60
Purchase #7	$209.69	13.549%	$238.1009	$238.10	$238.10	$238.10
7 purchase totals =	$1,066.36		$1,159.9358	$1,159.95	$1,159.95	$1,159.90