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	$80.92	10.337%	$89.2847	$89.28	$89.30	$89.30
Purchase #2	$224.33	7.681%	$241.5608	$241.56	$241.55	$241.60
Purchase #3	$236.59	5.726%	$250.1371	$250.14	$250.15	$250.10
Purchase #4	$131.69	8.414%	$142.7704	$142.77	$142.75	$142.80
Purchase #5	$116.79	11.567%	$130.2991	$130.30	$130.30	$130.30
Purchase #6	$128.67	8.246%	$139.2801	$139.28	$139.30	$139.30
Purchase #7	$69.33	10.127%	$76.351	$76.35	$76.35	$76.40
7 purchase totals =	$988.32		$1,069.6832	$1,069.68	$1,069.70	$1,069.80