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	$89.27	10.351%	$98.5103	$98.51	$98.50	$98.50
Purchase #2	$223.29	4.191%	$232.6481	$232.65	$232.65	$232.60
Purchase #3	$46.31	10.545%	$51.1934	$51.19	$51.20	$51.20
Purchase #4	$11.71	6.462%	$12.4667	$12.47	$12.45	$12.50
Purchase #5	$128.95	10.313%	$142.2486	$142.25	$142.25	$142.20
Purchase #6	$26.59	7.102%	$28.4784	$28.48	$28.50	$28.50
Purchase #7	$25.49	9.399%	$27.8858	$27.89	$27.90	$27.90
7 purchase totals =	$551.61		$593.4313	$593.44	$593.45	$593.40