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	$249.27	5.293%	$262.4639	$262.46	$262.45	$262.50
Purchase #2	$54.59	9.200%	$59.6123	$59.61	$59.60	$59.60
Purchase #3	$218.58	4.513%	$228.4445	$228.44	$228.45	$228.40
Purchase #4	$49.62	11.537%	$55.3447	$55.34	$55.35	$55.30
Purchase #5	$238.48	12.865%	$269.1605	$269.16	$269.15	$269.20
Purchase #6	$66.73	4.708%	$69.8716	$69.87	$69.85	$69.90
Purchase #7	$111.47	9.287%	$121.8222	$121.82	$121.80	$121.80
7 purchase totals =	$988.74		$1,066.7197	$1,066.70	$1,066.65	$1,066.70