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	$58.77	13.819%	$66.8914	$66.89	$66.90	$66.90
Purchase #2	$207.46	5.449%	$218.7645	$218.76	$218.75	$218.80
Purchase #3	$229.37	9.234%	$250.55	$250.55	$250.55	$250.60
Purchase #4	$238.48	3.202%	$246.1161	$246.12	$246.10	$246.10
Purchase #5	$118.87	7.244%	$127.4809	$127.48	$127.50	$127.50
Purchase #6	$184.25	6.833%	$196.8398	$196.84	$196.85	$196.80
Purchase #7	$183.73	8.244%	$198.8767	$198.88	$198.90	$198.90
7 purchase totals =	$1,220.93		$1,305.5194	$1,305.52	$1,305.55	$1,305.60