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	$76.95	6.677%	$82.088	$82.09	$82.10	$82.10
Purchase #2	$167.53	6.444%	$178.3256	$178.33	$178.35	$178.30
Purchase #3	$148.73	10.433%	$164.247	$164.25	$164.25	$164.20
Purchase #4	$59.33	11.122%	$65.9287	$65.93	$65.95	$65.90
Purchase #5	$28.28	5.418%	$29.8122	$29.81	$29.80	$29.80
Purchase #6	$142.72	10.855%	$158.2123	$158.21	$158.20	$158.20
Purchase #7	$136.96	3.543%	$141.8125	$141.81	$141.80	$141.80
7 purchase totals =	$760.50		$820.4263	$820.43	$820.45	$820.30