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	$33.27	6.662%	$35.4864	$35.49	$35.50	$35.50
Purchase #2	$164.95	12.654%	$185.8228	$185.82	$185.80	$185.80
Purchase #3	$30.44	5.649%	$32.1596	$32.16	$32.15	$32.20
Purchase #4	$212.51	7.260%	$227.9382	$227.94	$227.95	$227.90
Purchase #5	$99.41	8.178%	$107.5397	$107.54	$107.55	$107.50
Purchase #6	$39.47	8.588%	$42.8597	$42.86	$42.85	$42.90
Purchase #7	$66.60	3.567%	$68.9756	$68.98	$69.00	$69.00
7 purchase totals =	$646.65		$700.7820	$700.79	$700.80	$700.80