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	$104.37	13.347%	$118.3003	$118.30	$118.30	$118.30
Purchase #2	$228.61	6.553%	$243.5908	$243.59	$243.60	$243.60
Purchase #3	$66.27	10.109%	$72.9692	$72.97	$72.95	$73.00
Purchase #4	$148.38	12.202%	$166.4853	$166.49	$166.50	$166.50
Purchase #5	$245.76	9.460%	$269.0089	$269.01	$269.00	$269.00
Purchase #6	$157.83	9.754%	$173.2247	$173.22	$173.20	$173.20
Purchase #7	$77.72	7.777%	$83.7643	$83.76	$83.75	$83.80
7 purchase totals =	$1,028.94		$1,127.3435	$1,127.34	$1,127.30	$1,127.40