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	$215.94	10.355%	$238.3006	$238.30	$238.30	$238.30
Purchase #2	$124.57	4.640%	$130.35	$130.35	$130.35	$130.40
Purchase #3	$56.78	9.258%	$62.0367	$62.04	$62.05	$62.00
Purchase #4	$147.49	10.155%	$162.4676	$162.47	$162.45	$162.50
Purchase #5	$148.73	4.321%	$155.1566	$155.16	$155.15	$155.20
Purchase #6	$121.36	4.734%	$127.1052	$127.11	$127.10	$127.10
Purchase #7	$43.39	11.667%	$48.4523	$48.45	$48.45	$48.50
7 purchase totals =	$858.26		$923.8690	$923.88	$923.85	$924.00