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	$34.90	8.337%	$37.8096	$37.81	$37.80	$37.80
Purchase #2	$47.62	6.754%	$50.8363	$50.84	$50.85	$50.80
Purchase #3	$46.29	3.817%	$48.0569	$48.06	$48.05	$48.10
Purchase #4	$98.25	11.398%	$109.4485	$109.45	$109.45	$109.40
Purchase #5	$90.68	13.770%	$103.1666	$103.17	$103.15	$103.20
Purchase #6	$237.81	4.344%	$248.1405	$248.14	$248.15	$248.10
Purchase #7	$59.65	10.144%	$65.7009	$65.70	$65.70	$65.70
7 purchase totals =	$615.20		$663.1593	$663.17	$663.15	$663.10