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	$82.41	9.433%	$90.1837	$90.18	$90.20	$90.20
Purchase #2	$205.77	11.757%	$229.9624	$229.96	$229.95	$230.00
Purchase #3	$87.39	12.464%	$98.2823	$98.28	$98.30	$98.30
Purchase #4	$116.38	11.862%	$130.185	$130.19	$130.20	$130.20
Purchase #5	$198.66	4.463%	$207.5262	$207.53	$207.55	$207.50
Purchase #6	$80.54	11.487%	$89.7916	$89.79	$89.80	$89.80
Purchase #7	$159.96	3.319%	$165.2691	$165.27	$165.25	$165.30
7 purchase totals =	$931.11		$1,011.2003	$1,011.20	$1,011.25	$1,011.30