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	$200.50	11.698%	$223.9545	$223.95	$223.95	$224.00
Purchase #2	$71.75	9.167%	$78.3273	$78.33	$78.35	$78.30
Purchase #3	$49.58	12.855%	$55.9535	$55.95	$55.95	$56.00
Purchase #4	$66.46	13.431%	$75.3862	$75.39	$75.40	$75.40
Purchase #5	$185.26	5.401%	$195.2659	$195.27	$195.25	$195.30
Purchase #6	$238.84	4.333%	$249.1889	$249.19	$249.20	$249.20
Purchase #7	$200.93	10.499%	$222.0256	$222.03	$222.05	$222.00
7 purchase totals =	$1,013.32		$1,100.1019	$1,100.11	$1,100.15	$1,100.20