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	$56.84	4.734%	$59.5308	$59.53	$59.55	$59.50
Purchase #2	$79.91	10.470%	$88.2766	$88.28	$88.30	$88.30
Purchase #3	$226.26	12.816%	$255.2575	$255.26	$255.25	$255.30
Purchase #4	$51.86	6.109%	$55.0281	$55.03	$55.05	$55.00
Purchase #5	$131.97	4.689%	$138.1581	$138.16	$138.15	$138.20
Purchase #6	$206.61	11.168%	$229.6842	$229.68	$229.70	$229.70
Purchase #7	$163.58	4.818%	$171.4613	$171.46	$171.45	$171.50
7 purchase totals =	$917.03		$997.3966	$997.40	$997.45	$997.50