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	$184.95	3.221%	$190.9072	$190.91	$190.90	$190.90
Purchase #2	$60.31	11.741%	$67.391	$67.39	$67.40	$67.40
Purchase #3	$11.48	3.523%	$11.8844	$11.88	$11.90	$11.90
Purchase #4	$100.75	4.250%	$105.0319	$105.03	$105.05	$105.00
Purchase #5	$156.55	4.805%	$164.0722	$164.07	$164.05	$164.10
Purchase #6	$125.50	7.264%	$134.6163	$134.62	$134.60	$134.60
Purchase #7	$197.58	13.192%	$223.6448	$223.64	$223.65	$223.60
7 purchase totals =	$837.12		$897.5478	$897.54	$897.55	$897.50