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	$90.47	3.459%	$93.5994	$93.60	$93.60	$93.60
Purchase #2	$101.60	13.445%	$115.2601	$115.26	$115.25	$115.30
Purchase #3	$113.37	12.537%	$127.5832	$127.58	$127.60	$127.60
Purchase #4	$102.71	13.543%	$116.62	$116.62	$116.60	$116.60
Purchase #5	$74.27	8.441%	$80.5391	$80.54	$80.55	$80.50
Purchase #6	$225.76	12.296%	$253.5194	$253.52	$253.50	$253.50
Purchase #7	$54.44	9.518%	$59.6216	$59.62	$59.60	$59.60
7 purchase totals =	$762.62		$846.7428	$846.74	$846.70	$846.70