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	$89.94	10.209%	$99.122	$99.12	$99.10	$99.10
Purchase #2	$31.91	10.537%	$35.2724	$35.27	$35.25	$35.30
Purchase #3	$90.36	7.585%	$97.2138	$97.21	$97.20	$97.20
Purchase #4	$34.46	6.261%	$36.6175	$36.62	$36.60	$36.60
Purchase #5	$68.77	3.618%	$71.2581	$71.26	$71.25	$71.30
Purchase #6	$32.64	11.128%	$36.2722	$36.27	$36.25	$36.30
Purchase #7	$23.52	7.707%	$25.3327	$25.33	$25.35	$25.30
7 purchase totals =	$371.60		$401.0887	$401.08	$401.00	$401.10