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	$113.63	8.540%	$123.334	$123.33	$123.35	$123.30
Purchase #2	$134.81	5.822%	$142.6586	$142.66	$142.65	$142.70
Purchase #3	$242.47	5.829%	$256.6036	$256.60	$256.60	$256.60
Purchase #4	$227.83	13.784%	$259.2341	$259.23	$259.25	$259.20
Purchase #5	$141.37	4.290%	$147.4348	$147.43	$147.45	$147.40
Purchase #6	$225.99	7.220%	$242.3065	$242.31	$242.30	$242.30
Purchase #7	$106.33	3.403%	$109.9484	$109.95	$109.95	$109.90
7 purchase totals =	$1,192.43		$1,281.5200	$1,281.51	$1,281.55	$1,281.40