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	$165.82	4.683%	$173.5854	$173.59	$173.60	$173.60
Purchase #2	$42.77	7.206%	$45.852	$45.85	$45.85	$45.90
Purchase #3	$167.78	12.637%	$188.9824	$188.98	$189.00	$189.00
Purchase #4	$72.34	13.512%	$82.1146	$82.11	$82.10	$82.10
Purchase #5	$5.83	10.340%	$6.4328	$6.43	$6.45	$6.40
Purchase #6	$166.41	13.851%	$189.4594	$189.46	$189.45	$189.50
Purchase #7	$89.91	4.302%	$93.7779	$93.78	$93.80	$93.80
7 purchase totals =	$710.86		$780.2045	$780.20	$780.25	$780.30