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	$158.63	7.460%	$170.4638	$170.46	$170.45	$170.50
Purchase #2	$187.48	4.167%	$195.2923	$195.29	$195.30	$195.30
Purchase #3	$130.35	6.799%	$139.2125	$139.21	$139.20	$139.20
Purchase #4	$79.28	3.124%	$81.7567	$81.76	$81.75	$81.80
Purchase #5	$81.32	10.553%	$89.9017	$89.90	$89.90	$89.90
Purchase #6	$247.98	13.107%	$280.4827	$280.48	$280.50	$280.50
Purchase #7	$55.92	10.848%	$61.9862	$61.99	$62.00	$62.00
7 purchase totals =	$940.96		$1,019.0959	$1,019.09	$1,019.10	$1,019.20