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	$172.69	12.839%	$194.8617	$194.86	$194.85	$194.90
Purchase #2	$9.42	11.710%	$10.5231	$10.52	$10.50	$10.50
Purchase #3	$5.73	13.130%	$6.4823	$6.48	$6.50	$6.50
Purchase #4	$161.74	5.173%	$170.1068	$170.11	$170.10	$170.10
Purchase #5	$147.95	5.672%	$156.3417	$156.34	$156.35	$156.30
Purchase #6	$22.77	3.152%	$23.4877	$23.49	$23.50	$23.50
Purchase #7	$70.66	10.459%	$78.0503	$78.05	$78.05	$78.10
7 purchase totals =	$590.96		$639.8536	$639.85	$639.85	$639.90