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	$49.40	12.353%	$55.5024	$55.50	$55.50	$55.50
Purchase #2	$193.94	12.547%	$218.2737	$218.27	$218.25	$218.30
Purchase #3	$230.36	12.123%	$258.2865	$258.29	$258.30	$258.30
Purchase #4	$67.64	5.662%	$71.4698	$71.47	$71.45	$71.50
Purchase #5	$179.88	6.245%	$191.1135	$191.11	$191.10	$191.10
Purchase #6	$115.32	4.482%	$120.4886	$120.49	$120.50	$120.50
Purchase #7	$163.53	12.471%	$183.9238	$183.92	$183.90	$183.90
7 purchase totals =	$1,000.07		$1,099.0583	$1,099.05	$1,099.00	$1,099.10