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	$80.72	10.258%	$89.0003	$89.00	$89.00	$89.00
Purchase #2	$213.30	7.720%	$229.7668	$229.77	$229.75	$229.80
Purchase #3	$103.58	8.161%	$112.0332	$112.03	$112.05	$112.00
Purchase #4	$59.44	12.415%	$66.8195	$66.82	$66.80	$66.80
Purchase #5	$123.72	5.118%	$130.052	$130.05	$130.05	$130.10
Purchase #6	$239.77	3.807%	$248.898	$248.90	$248.90	$248.90
Purchase #7	$231.30	8.565%	$251.1108	$251.11	$251.10	$251.10
7 purchase totals =	$1,051.83		$1,127.6806	$1,127.68	$1,127.65	$1,127.70