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	$127.26	3.614%	$131.8592	$131.86	$131.85	$131.90
Purchase #2	$155.65	10.400%	$171.8376	$171.84	$171.85	$171.80
Purchase #3	$27.43	9.591%	$30.0608	$30.06	$30.05	$30.10
Purchase #4	$78.50	5.488%	$82.8081	$82.81	$82.80	$82.80
Purchase #5	$60.34	12.325%	$67.7769	$67.78	$67.80	$67.80
Purchase #6	$134.43	13.405%	$152.4503	$152.45	$152.45	$152.50
Purchase #7	$48.25	6.267%	$51.2738	$51.27	$51.25	$51.30
7 purchase totals =	$631.86		$688.0667	$688.07	$688.05	$688.20