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	$98.53	4.388%	$102.8535	$102.85	$102.85	$102.90
Purchase #2	$156.91	8.270%	$169.8865	$169.89	$169.90	$169.90
Purchase #3	$41.86	3.735%	$43.4235	$43.42	$43.40	$43.40
Purchase #4	$34.63	9.734%	$38.0009	$38.00	$38.00	$38.00
Purchase #5	$42.45	7.259%	$45.5314	$45.53	$45.55	$45.50
Purchase #6	$56.85	7.548%	$61.141	$61.14	$61.15	$61.10
Purchase #7	$40.67	13.797%	$46.2812	$46.28	$46.30	$46.30
7 purchase totals =	$471.90		$507.1180	$507.11	$507.15	$507.10