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	$248.28	6.556%	$264.5572	$264.56	$264.55	$264.60
Purchase #2	$58.64	6.695%	$62.5659	$62.57	$62.55	$62.60
Purchase #3	$191.44	4.208%	$199.4958	$199.50	$199.50	$199.50
Purchase #4	$61.92	9.420%	$67.7529	$67.75	$67.75	$67.80
Purchase #5	$116.37	10.383%	$128.4527	$128.45	$128.45	$128.50
Purchase #6	$123.50	4.443%	$128.9871	$128.99	$129.00	$129.00
Purchase #7	$39.67	6.433%	$42.222	$42.22	$42.20	$42.20
7 purchase totals =	$839.82		$894.0336	$894.04	$894.00	$894.20