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	$248.36	12.547%	$279.5217	$279.52	$279.50	$279.50
Purchase #2	$97.45	3.472%	$100.8335	$100.83	$100.85	$100.80
Purchase #3	$63.97	11.488%	$71.3189	$71.32	$71.30	$71.30
Purchase #4	$122.47	4.707%	$128.2347	$128.23	$128.25	$128.20
Purchase #5	$244.91	9.158%	$267.3389	$267.34	$267.35	$267.30
Purchase #6	$35.99	9.328%	$39.3471	$39.35	$39.35	$39.30
Purchase #7	$222.33	3.374%	$229.8314	$229.83	$229.85	$229.80
7 purchase totals =	$1,035.48		$1,116.4262	$1,116.42	$1,116.45	$1,116.20