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	$236.54	6.747%	$252.4994	$252.50	$252.50	$252.50
Purchase #2	$36.64	10.789%	$40.5931	$40.59	$40.60	$40.60
Purchase #3	$91.80	5.402%	$96.759	$96.76	$96.75	$96.80
Purchase #4	$83.65	3.758%	$86.7936	$86.79	$86.80	$86.80
Purchase #5	$39.34	10.166%	$43.3393	$43.34	$43.35	$43.30
Purchase #6	$90.88	9.217%	$99.2564	$99.26	$99.25	$99.30
Purchase #7	$19.49	5.403%	$20.543	$20.54	$20.55	$20.50
7 purchase totals =	$598.34		$639.7838	$639.78	$639.80	$639.80