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	$179.72	11.587%	$200.5442	$200.54	$200.55	$200.50
Purchase #2	$52.43	6.678%	$55.9313	$55.93	$55.95	$55.90
Purchase #3	$150.48	3.225%	$155.333	$155.33	$155.35	$155.30
Purchase #4	$221.84	7.613%	$238.7287	$238.73	$238.75	$238.70
Purchase #5	$97.68	6.779%	$104.3017	$104.30	$104.30	$104.30
Purchase #6	$153.47	8.153%	$165.9824	$165.98	$166.00	$166.00
Purchase #7	$75.33	3.438%	$77.9198	$77.92	$77.90	$77.90
7 purchase totals =	$930.95		$998.7411	$998.73	$998.80	$998.60