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	$105.56	6.594%	$112.5206	$112.52	$112.50	$112.50
Purchase #2	$227.66	11.842%	$254.6195	$254.62	$254.60	$254.60
Purchase #3	$13.62	5.295%	$14.3412	$14.34	$14.35	$14.30
Purchase #4	$79.31	3.450%	$82.0462	$82.05	$82.05	$82.00
Purchase #5	$203.30	7.764%	$219.0842	$219.08	$219.10	$219.10
Purchase #6	$134.55	8.397%	$145.8482	$145.85	$145.85	$145.80
Purchase #7	$199.82	7.712%	$215.2301	$215.23	$215.25	$215.20
7 purchase totals =	$963.82		$1,043.6900	$1,043.69	$1,043.70	$1,043.50