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	$86.85	3.150%	$89.5858	$89.59	$89.60	$89.60
Purchase #2	$121.81	8.133%	$131.7168	$131.72	$131.70	$131.70
Purchase #3	$54.32	7.289%	$58.2794	$58.28	$58.30	$58.30
Purchase #4	$118.61	10.322%	$130.8529	$130.85	$130.85	$130.90
Purchase #5	$226.46	8.296%	$245.2471	$245.25	$245.25	$245.20
Purchase #6	$240.98	8.788%	$262.1573	$262.16	$262.15	$262.20
Purchase #7	$48.97	8.371%	$53.0693	$53.07	$53.05	$53.10
7 purchase totals =	$898.00		$970.9086	$970.92	$970.90	$971.00