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	$139.34	12.863%	$157.2633	$157.26	$157.25	$157.30
Purchase #2	$209.50	6.152%	$222.3884	$222.39	$222.40	$222.40
Purchase #3	$174.89	9.717%	$191.8841	$191.88	$191.90	$191.90
Purchase #4	$190.49	3.319%	$196.8124	$196.81	$196.80	$196.80
Purchase #5	$134.64	8.152%	$145.6159	$145.62	$145.60	$145.60
Purchase #6	$222.79	12.714%	$251.1155	$251.12	$251.10	$251.10
Purchase #7	$101.81	8.819%	$110.7886	$110.79	$110.80	$110.80
7 purchase totals =	$1,173.46		$1,275.8682	$1,275.87	$1,275.85	$1,275.90