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	$193.92	12.872%	$218.8814	$218.88	$218.90	$218.90
Purchase #2	$242.75	3.111%	$250.302	$250.30	$250.30	$250.30
Purchase #3	$71.84	10.172%	$79.1476	$79.15	$79.15	$79.10
Purchase #4	$239.89	3.426%	$248.1086	$248.11	$248.10	$248.10
Purchase #5	$214.47	11.475%	$239.0804	$239.08	$239.10	$239.10
Purchase #6	$92.77	8.199%	$100.3762	$100.38	$100.40	$100.40
Purchase #7	$29.45	10.179%	$32.4477	$32.45	$32.45	$32.40
7 purchase totals =	$1,085.09		$1,168.3439	$1,168.35	$1,168.40	$1,168.30