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	$83.64	7.471%	$89.8887	$89.89	$89.90	$89.90
Purchase #2	$238.69	4.335%	$249.0372	$249.04	$249.05	$249.00
Purchase #3	$133.87	7.602%	$144.0468	$144.05	$144.05	$144.00
Purchase #4	$57.37	4.307%	$59.8409	$59.84	$59.85	$59.80
Purchase #5	$143.64	4.533%	$150.1512	$150.15	$150.15	$150.20
Purchase #6	$156.47	12.249%	$175.636	$175.64	$175.65	$175.60
Purchase #7	$208.43	4.842%	$218.5222	$218.52	$218.50	$218.50
7 purchase totals =	$1,022.11		$1,087.1230	$1,087.13	$1,087.15	$1,087.00