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	$40.37	10.251%	$44.5083	$44.51	$44.50	$44.50
Purchase #2	$20.78	11.689%	$23.209	$23.21	$23.20	$23.20
Purchase #3	$120.53	5.837%	$127.5653	$127.57	$127.55	$127.60
Purchase #4	$151.90	12.465%	$170.8343	$170.83	$170.85	$170.80
Purchase #5	$56.79	4.734%	$59.4784	$59.48	$59.50	$59.50
Purchase #6	$213.48	8.109%	$230.7911	$230.79	$230.80	$230.80
Purchase #7	$63.82	13.636%	$72.5225	$72.52	$72.50	$72.50
7 purchase totals =	$667.67		$728.9089	$728.91	$728.90	$728.90