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	$42.77	4.269%	$44.5959	$44.60	$44.60	$44.60
Purchase #2	$55.86	3.383%	$57.7497	$57.75	$57.75	$57.70
Purchase #3	$127.83	10.723%	$141.5372	$141.54	$141.55	$141.50
Purchase #4	$115.96	7.335%	$124.4657	$124.47	$124.45	$124.50
Purchase #5	$178.98	9.701%	$196.3428	$196.34	$196.35	$196.30
Purchase #6	$102.38	13.803%	$116.5115	$116.51	$116.50	$116.50
Purchase #7	$127.40	9.823%	$139.9145	$139.91	$139.90	$139.90
7 purchase totals =	$751.18		$821.1173	$821.12	$821.10	$821.00