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	$118.88	3.589%	$123.1466	$123.15	$123.15	$123.10
Purchase #2	$151.84	9.865%	$166.819	$166.82	$166.80	$166.80
Purchase #3	$77.40	10.561%	$85.5742	$85.57	$85.55	$85.60
Purchase #4	$172.32	11.365%	$191.9042	$191.90	$191.90	$191.90
Purchase #5	$129.42	3.166%	$133.5174	$133.52	$133.50	$133.50
Purchase #6	$102.55	7.683%	$110.4289	$110.43	$110.45	$110.40
Purchase #7	$73.70	13.636%	$83.7497	$83.75	$83.75	$83.70
7 purchase totals =	$826.11		$895.1400	$895.14	$895.10	$895.00