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	$166.64	3.686%	$172.7824	$172.78	$172.80	$172.80
Purchase #2	$93.83	11.117%	$104.2611	$104.26	$104.25	$104.30
Purchase #3	$78.59	5.113%	$82.6083	$82.61	$82.60	$82.60
Purchase #4	$202.99	5.514%	$214.1829	$214.18	$214.20	$214.20
Purchase #5	$226.81	10.551%	$250.7407	$250.74	$250.75	$250.70
Purchase #6	$134.86	5.326%	$142.0426	$142.04	$142.05	$142.00
Purchase #7	$92.55	12.192%	$103.8337	$103.83	$103.85	$103.80
7 purchase totals =	$996.27		$1,070.4517	$1,070.44	$1,070.50	$1,070.40