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	$48.77	12.838%	$55.0311	$55.03	$55.05	$55.00
Purchase #2	$47.92	11.287%	$53.3287	$53.33	$53.35	$53.30
Purchase #3	$46.94	13.400%	$53.23	$53.23	$53.25	$53.20
Purchase #4	$137.93	10.531%	$152.4554	$152.46	$152.45	$152.50
Purchase #5	$203.38	13.750%	$231.3448	$231.34	$231.35	$231.30
Purchase #6	$166.69	5.255%	$175.4496	$175.45	$175.45	$175.40
Purchase #7	$79.95	11.683%	$89.2906	$89.29	$89.30	$89.30
7 purchase totals =	$731.58		$810.1302	$810.13	$810.20	$810.00