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	$173.27	7.798%	$186.7816	$186.78	$186.80	$186.80
Purchase #2	$240.84	11.435%	$268.3801	$268.38	$268.40	$268.40
Purchase #3	$93.61	7.771%	$100.8844	$100.88	$100.90	$100.90
Purchase #4	$10.64	11.723%	$11.8873	$11.89	$11.90	$11.90
Purchase #5	$236.51	4.857%	$247.9973	$248.00	$248.00	$248.00
Purchase #6	$125.30	11.432%	$139.6243	$139.62	$139.60	$139.60
Purchase #7	$49.69	10.409%	$54.8622	$54.86	$54.85	$54.90
7 purchase totals =	$929.86		$1,010.4172	$1,010.41	$1,010.45	$1,010.50