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	$70.73	13.325%	$80.1548	$80.15	$80.15	$80.20
Purchase #2	$50.42	9.208%	$55.0627	$55.06	$55.05	$55.10
Purchase #3	$31.84	10.142%	$35.0692	$35.07	$35.05	$35.10
Purchase #4	$178.47	11.504%	$199.0012	$199.00	$199.00	$199.00
Purchase #5	$55.59	6.151%	$59.0093	$59.01	$59.00	$59.00
Purchase #6	$216.75	9.356%	$237.0291	$237.03	$237.05	$237.00
Purchase #7	$74.94	5.226%	$78.8564	$78.86	$78.85	$78.90
7 purchase totals =	$678.74		$744.1827	$744.18	$744.15	$744.30