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	$156.38	10.589%	$172.9391	$172.94	$172.95	$172.90
Purchase #2	$199.60	12.329%	$224.2087	$224.21	$224.20	$224.20
Purchase #3	$138.77	7.338%	$148.9529	$148.95	$148.95	$149.00
Purchase #4	$79.69	12.180%	$89.3962	$89.40	$89.40	$89.40
Purchase #5	$191.55	9.424%	$209.6017	$209.60	$209.60	$209.60
Purchase #6	$244.69	11.512%	$272.8587	$272.86	$272.85	$272.90
Purchase #7	$77.65	6.777%	$82.9123	$82.91	$82.90	$82.90
7 purchase totals =	$1,088.33		$1,200.8696	$1,200.87	$1,200.85	$1,200.90