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	$40.89	12.218%	$45.8859	$45.89	$45.90	$45.90
Purchase #2	$81.45	10.133%	$89.7033	$89.70	$89.70	$89.70
Purchase #3	$123.76	12.285%	$138.9639	$138.96	$138.95	$139.00
Purchase #4	$96.67	3.144%	$99.7093	$99.71	$99.70	$99.70
Purchase #5	$181.59	9.766%	$199.3241	$199.32	$199.30	$199.30
Purchase #6	$220.84	9.574%	$241.9832	$241.98	$242.00	$242.00
Purchase #7	$104.54	9.627%	$114.6041	$114.60	$114.60	$114.60
7 purchase totals =	$849.74		$930.1738	$930.16	$930.15	$930.20