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	$38.94	7.792%	$41.9742	$41.97	$41.95	$42.00
Purchase #2	$111.61	8.715%	$121.3368	$121.34	$121.35	$121.30
Purchase #3	$115.41	10.321%	$127.3215	$127.32	$127.30	$127.30
Purchase #4	$107.35	8.568%	$116.5477	$116.55	$116.55	$116.50
Purchase #5	$116.56	12.320%	$130.9202	$130.92	$130.90	$130.90
Purchase #6	$77.32	3.312%	$79.8808	$79.88	$79.90	$79.90
Purchase #7	$154.97	7.325%	$166.3216	$166.32	$166.30	$166.30
7 purchase totals =	$722.16		$784.3028	$784.30	$784.25	$784.20