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	$158.99	5.208%	$167.2702	$167.27	$167.25	$167.30
Purchase #2	$188.57	6.326%	$200.4989	$200.50	$200.50	$200.50
Purchase #3	$99.26	12.749%	$111.9147	$111.91	$111.90	$111.90
Purchase #4	$60.50	8.167%	$65.441	$65.44	$65.45	$65.40
Purchase #5	$113.43	7.489%	$121.9248	$121.92	$121.90	$121.90
Purchase #6	$31.77	12.637%	$35.7848	$35.78	$35.80	$35.80
Purchase #7	$219.39	4.617%	$229.5192	$229.52	$229.50	$229.50
7 purchase totals =	$871.91		$932.3536	$932.34	$932.30	$932.30