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	$26.60	4.186%	$27.7135	$27.71	$27.70	$27.70
Purchase #2	$133.93	9.307%	$146.3949	$146.39	$146.40	$146.40
Purchase #3	$31.58	5.404%	$33.2866	$33.29	$33.30	$33.30
Purchase #4	$67.93	13.344%	$76.9946	$76.99	$77.00	$77.00
Purchase #5	$158.44	11.415%	$176.5259	$176.53	$176.55	$176.50
Purchase #6	$120.82	5.840%	$127.8759	$127.88	$127.90	$127.90
Purchase #7	$154.33	5.267%	$162.4586	$162.46	$162.45	$162.50
7 purchase totals =	$693.63		$751.2500	$751.25	$751.30	$751.30