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	$72.27	7.376%	$77.6006	$77.60	$77.60	$77.60
Purchase #2	$241.90	5.325%	$254.7812	$254.78	$254.80	$254.80
Purchase #3	$215.50	9.281%	$235.5006	$235.50	$235.50	$235.50
Purchase #4	$93.90	7.347%	$100.7988	$100.80	$100.80	$100.80
Purchase #5	$6.82	13.546%	$7.7438	$7.74	$7.75	$7.70
Purchase #6	$75.64	6.580%	$80.6171	$80.62	$80.60	$80.60
Purchase #7	$209.94	5.494%	$221.4741	$221.47	$221.45	$221.50
7 purchase totals =	$915.97		$978.5162	$978.51	$978.50	$978.50