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	$90.47	10.714%	$100.163	$100.16	$100.15	$100.20
Purchase #2	$109.57	5.607%	$115.7136	$115.71	$115.70	$115.70
Purchase #3	$213.56	9.604%	$234.0703	$234.07	$234.05	$234.10
Purchase #4	$236.42	3.234%	$244.0658	$244.07	$244.05	$244.10
Purchase #5	$214.44	5.401%	$226.0219	$226.02	$226.00	$226.00
Purchase #6	$143.82	13.262%	$162.8934	$162.89	$162.90	$162.90
Purchase #7	$86.76	4.782%	$90.9089	$90.91	$90.90	$90.90
7 purchase totals =	$1,095.04		$1,173.8369	$1,173.83	$1,173.75	$1,173.90