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	$17.75	3.215%	$18.3207	$18.32	$18.30	$18.30
Purchase #2	$197.56	12.247%	$221.7552	$221.76	$221.75	$221.80
Purchase #3	$196.27	13.119%	$222.0187	$222.02	$222.00	$222.00
Purchase #4	$51.52	6.770%	$55.0079	$55.01	$55.00	$55.00
Purchase #5	$10.84	6.365%	$11.53	$11.53	$11.55	$11.50
Purchase #6	$136.87	9.218%	$149.4867	$149.49	$149.50	$149.50
Purchase #7	$200.30	11.571%	$223.4767	$223.48	$223.50	$223.50
7 purchase totals =	$811.11		$901.5959	$901.61	$901.60	$901.60