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	$184.72	10.163%	$203.4931	$203.49	$203.50	$203.50
Purchase #2	$30.84	5.400%	$32.5054	$32.51	$32.50	$32.50
Purchase #3	$221.27	5.453%	$233.3359	$233.34	$233.35	$233.30
Purchase #4	$82.96	7.608%	$89.2716	$89.27	$89.25	$89.30
Purchase #5	$145.52	12.628%	$163.8963	$163.90	$163.90	$163.90
Purchase #6	$95.34	11.214%	$106.0314	$106.03	$106.05	$106.00
Purchase #7	$180.53	5.664%	$190.7552	$190.76	$190.75	$190.80
7 purchase totals =	$941.18		$1,019.2889	$1,019.30	$1,019.30	$1,019.30