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	$28.52	10.504%	$31.5157	$31.52	$31.50	$31.50
Purchase #2	$140.92	5.357%	$148.4691	$148.47	$148.45	$148.50
Purchase #3	$209.28	9.329%	$228.8037	$228.80	$228.80	$228.80
Purchase #4	$58.68	4.600%	$61.3793	$61.38	$61.40	$61.40
Purchase #5	$124.74	11.140%	$138.636	$138.64	$138.65	$138.60
Purchase #6	$219.57	12.688%	$247.429	$247.43	$247.45	$247.40
Purchase #7	$145.67	9.739%	$159.8568	$159.86	$159.85	$159.90
7 purchase totals =	$927.38		$1,016.0896	$1,016.10	$1,016.10	$1,016.10