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	$181.88	9.237%	$198.6803	$198.68	$198.70	$198.70
Purchase #2	$152.87	10.854%	$169.4625	$169.46	$169.45	$169.50
Purchase #3	$82.46	9.219%	$90.062	$90.06	$90.05	$90.10
Purchase #4	$116.51	13.179%	$131.8649	$131.86	$131.85	$131.90
Purchase #5	$151.90	10.361%	$167.6384	$167.64	$167.65	$167.60
Purchase #6	$10.89	10.428%	$12.0256	$12.03	$12.05	$12.00
Purchase #7	$46.95	8.572%	$50.9746	$50.97	$50.95	$51.00
7 purchase totals =	$743.46		$820.7083	$820.70	$820.70	$820.80