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	$54.25	6.114%	$57.5668	$57.57	$57.55	$57.60
Purchase #2	$129.97	6.362%	$138.2387	$138.24	$138.25	$138.20
Purchase #3	$57.91	13.143%	$65.5211	$65.52	$65.50	$65.50
Purchase #4	$91.69	12.799%	$103.4254	$103.43	$103.45	$103.40
Purchase #5	$222.25	10.508%	$245.604	$245.60	$245.60	$245.60
Purchase #6	$197.44	9.641%	$216.4752	$216.48	$216.50	$216.50
Purchase #7	$74.56	10.164%	$82.1383	$82.14	$82.15	$82.10
7 purchase totals =	$828.07		$908.9695	$908.98	$909.00	$908.90