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	$160.89	5.701%	$170.0623	$170.06	$170.05	$170.10
Purchase #2	$72.48	5.413%	$76.4033	$76.40	$76.40	$76.40
Purchase #3	$81.70	9.555%	$89.5064	$89.51	$89.50	$89.50
Purchase #4	$14.60	13.739%	$16.6059	$16.61	$16.60	$16.60
Purchase #5	$80.26	9.748%	$88.0837	$88.08	$88.10	$88.10
Purchase #6	$92.69	13.872%	$105.548	$105.55	$105.55	$105.50
Purchase #7	$43.48	7.206%	$46.6132	$46.61	$46.60	$46.60
7 purchase totals =	$546.10		$592.8228	$592.82	$592.80	$592.80