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	$109.28	13.221%	$123.7279	$123.73	$123.75	$123.70
Purchase #2	$130.69	7.677%	$140.7231	$140.72	$140.70	$140.70
Purchase #3	$46.39	11.404%	$51.6803	$51.68	$51.70	$51.70
Purchase #4	$61.57	9.453%	$67.3902	$67.39	$67.40	$67.40
Purchase #5	$52.59	7.649%	$56.6126	$56.61	$56.60	$56.60
Purchase #6	$27.58	11.172%	$30.6612	$30.66	$30.65	$30.70
Purchase #7	$54.84	4.137%	$57.1087	$57.11	$57.10	$57.10
7 purchase totals =	$482.94		$527.9040	$527.90	$527.90	$527.90