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	$36.50	7.197%	$39.1269	$39.13	$39.15	$39.10
Purchase #2	$78.64	10.449%	$86.8571	$86.86	$86.85	$86.90
Purchase #3	$57.45	5.131%	$60.3978	$60.40	$60.40	$60.40
Purchase #4	$172.40	10.521%	$190.5382	$190.54	$190.55	$190.50
Purchase #5	$137.57	10.391%	$151.8649	$151.86	$151.85	$151.90
Purchase #6	$101.43	8.191%	$109.7381	$109.74	$109.75	$109.70
Purchase #7	$197.53	3.158%	$203.768	$203.77	$203.75	$203.80
7 purchase totals =	$781.52		$842.2910	$842.30	$842.30	$842.30