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	$86.44	4.531%	$90.3566	$90.36	$90.35	$90.40
Purchase #2	$207.72	8.453%	$225.2786	$225.28	$225.30	$225.30
Purchase #3	$242.98	13.334%	$275.379	$275.38	$275.40	$275.40
Purchase #4	$153.31	9.327%	$167.6092	$167.61	$167.60	$167.60
Purchase #5	$128.33	11.521%	$143.1149	$143.11	$143.10	$143.10
Purchase #6	$109.44	13.777%	$124.5175	$124.52	$124.50	$124.50
Purchase #7	$135.83	12.787%	$153.1986	$153.20	$153.20	$153.20
7 purchase totals =	$1,064.05		$1,179.4544	$1,179.46	$1,179.45	$1,179.50