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	$37.44	8.723%	$40.7059	$40.71	$40.70	$40.70
Purchase #2	$26.94	4.576%	$28.1728	$28.17	$28.15	$28.20
Purchase #3	$160.25	4.607%	$167.6327	$167.63	$167.65	$167.60
Purchase #4	$229.73	9.655%	$251.9104	$251.91	$251.90	$251.90
Purchase #5	$241.99	8.357%	$262.2131	$262.21	$262.20	$262.20
Purchase #6	$52.89	13.255%	$59.9006	$59.90	$59.90	$59.90
Purchase #7	$70.72	13.593%	$80.333	$80.33	$80.35	$80.30
7 purchase totals =	$819.96		$890.8685	$890.86	$890.85	$890.80