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	$32.36	7.579%	$34.8126	$34.81	$34.80	$34.80
Purchase #2	$145.45	13.322%	$164.8268	$164.83	$164.85	$164.80
Purchase #3	$123.68	4.183%	$128.8535	$128.85	$128.85	$128.90
Purchase #4	$240.31	7.796%	$259.0446	$259.04	$259.05	$259.00
Purchase #5	$121.67	7.469%	$130.7575	$130.76	$130.75	$130.80
Purchase #6	$38.31	13.279%	$43.3972	$43.40	$43.40	$43.40
Purchase #7	$240.36	11.748%	$268.5975	$268.60	$268.60	$268.60
7 purchase totals =	$942.14		$1,030.2897	$1,030.29	$1,030.30	$1,030.30