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	$12.60	10.389%	$13.909	$13.91	$13.90	$13.90
Purchase #2	$90.40	10.572%	$99.9571	$99.96	$99.95	$100.00
Purchase #3	$72.28	8.735%	$78.5937	$78.59	$78.60	$78.60
Purchase #4	$54.64	6.430%	$58.1534	$58.15	$58.15	$58.20
Purchase #5	$6.77	11.148%	$7.5247	$7.52	$7.50	$7.50
Purchase #6	$175.40	6.259%	$186.3783	$186.38	$186.40	$186.40
Purchase #7	$20.43	7.795%	$22.0225	$22.02	$22.00	$22.00
7 purchase totals =	$432.52		$466.5387	$466.53	$466.50	$466.60