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	$18.94	11.531%	$21.124	$21.12	$21.10	$21.10
Purchase #2	$227.69	9.257%	$248.7673	$248.77	$248.75	$248.80
Purchase #3	$35.29	8.295%	$38.2173	$38.22	$38.20	$38.20
Purchase #4	$67.27	4.497%	$70.2951	$70.30	$70.30	$70.30
Purchase #5	$67.74	5.579%	$71.5192	$71.52	$71.50	$71.50
Purchase #6	$184.84	3.435%	$191.1893	$191.19	$191.20	$191.20
Purchase #7	$158.41	4.440%	$165.4434	$165.44	$165.45	$165.40
7 purchase totals =	$760.18		$806.5556	$806.56	$806.50	$806.50