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	$103.53	11.519%	$115.4556	$115.46	$115.45	$115.50
Purchase #2	$229.52	12.623%	$258.4923	$258.49	$258.50	$258.50
Purchase #3	$43.80	12.209%	$49.1475	$49.15	$49.15	$49.10
Purchase #4	$95.69	8.279%	$103.6122	$103.61	$103.60	$103.60
Purchase #5	$241.88	5.807%	$255.926	$255.93	$255.95	$255.90
Purchase #6	$242.25	13.576%	$275.1379	$275.14	$275.15	$275.10
Purchase #7	$137.69	3.131%	$142.0011	$142.00	$142.00	$142.00
7 purchase totals =	$1,094.36		$1,199.7726	$1,199.78	$1,199.80	$1,199.70