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	$31.43	12.461%	$35.3465	$35.35	$35.35	$35.30
Purchase #2	$130.86	11.494%	$145.901	$145.90	$145.90	$145.90
Purchase #3	$249.99	10.292%	$275.719	$275.72	$275.70	$275.70
Purchase #4	$148.38	4.458%	$154.9948	$154.99	$155.00	$155.00
Purchase #5	$68.69	3.671%	$71.2116	$71.21	$71.20	$71.20
Purchase #6	$105.56	3.844%	$109.6177	$109.62	$109.60	$109.60
Purchase #7	$213.63	11.452%	$238.0949	$238.09	$238.10	$238.10
7 purchase totals =	$948.54		$1,030.8855	$1,030.88	$1,030.85	$1,030.80