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	$245.82	4.548%	$256.9999	$257.00	$257.00	$257.00
Purchase #2	$130.90	13.129%	$148.0859	$148.09	$148.10	$148.10
Purchase #3	$38.74	8.668%	$42.098	$42.10	$42.10	$42.10
Purchase #4	$75.41	7.820%	$81.3071	$81.31	$81.30	$81.30
Purchase #5	$79.88	3.774%	$82.8947	$82.89	$82.90	$82.90
Purchase #6	$149.28	8.789%	$162.4002	$162.40	$162.40	$162.40
Purchase #7	$41.47	9.284%	$45.3201	$45.32	$45.30	$45.30
7 purchase totals =	$761.50		$819.1059	$819.11	$819.10	$819.10