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	$153.49	5.813%	$162.4124	$162.41	$162.40	$162.40
Purchase #2	$202.73	9.738%	$222.4718	$222.47	$222.45	$222.50
Purchase #3	$19.61	4.540%	$20.5003	$20.50	$20.50	$20.50
Purchase #4	$183.57	7.234%	$196.8495	$196.85	$196.85	$196.80
Purchase #5	$173.67	3.317%	$179.4306	$179.43	$179.45	$179.40
Purchase #6	$68.95	7.482%	$74.1088	$74.11	$74.10	$74.10
Purchase #7	$24.55	12.664%	$27.659	$27.66	$27.65	$27.70
7 purchase totals =	$826.57		$883.4324	$883.43	$883.40	$883.40