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	$240.27	12.276%	$269.7655	$269.77	$269.75	$269.80
Purchase #2	$179.85	6.541%	$191.614	$191.61	$191.60	$191.60
Purchase #3	$65.39	8.825%	$71.1607	$71.16	$71.15	$71.20
Purchase #4	$127.71	9.686%	$140.08	$140.08	$140.10	$140.10
Purchase #5	$231.38	3.216%	$238.8212	$238.82	$238.80	$238.80
Purchase #6	$146.98	6.838%	$157.0305	$157.03	$157.05	$157.00
Purchase #7	$67.40	12.632%	$75.914	$75.91	$75.90	$75.90
7 purchase totals =	$1,058.98		$1,144.3859	$1,144.38	$1,144.35	$1,144.40