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	$85.70	6.470%	$91.2448	$91.24	$91.25	$91.20
Purchase #2	$40.75	3.475%	$42.1661	$42.17	$42.15	$42.20
Purchase #3	$215.42	10.519%	$238.08	$238.08	$238.10	$238.10
Purchase #4	$126.84	5.872%	$134.288	$134.29	$134.30	$134.30
Purchase #5	$240.97	12.653%	$271.4599	$271.46	$271.45	$271.50
Purchase #6	$67.93	4.389%	$70.9114	$70.91	$70.90	$70.90
Purchase #7	$37.61	12.479%	$42.3034	$42.30	$42.30	$42.30
7 purchase totals =	$815.22		$890.4536	$890.45	$890.45	$890.50