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	$134.41	3.183%	$138.6883	$138.69	$138.70	$138.70
Purchase #2	$40.56	5.778%	$42.9036	$42.90	$42.90	$42.90
Purchase #3	$186.51	5.349%	$196.4864	$196.49	$196.50	$196.50
Purchase #4	$198.68	10.852%	$220.2408	$220.24	$220.25	$220.20
Purchase #5	$212.80	9.742%	$233.531	$233.53	$233.55	$233.50
Purchase #6	$217.29	11.663%	$242.6325	$242.63	$242.65	$242.60
Purchase #7	$209.33	7.762%	$225.5782	$225.58	$225.60	$225.60
7 purchase totals =	$1,199.58		$1,300.0608	$1,300.06	$1,300.15	$1,300.00