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	$167.40	6.761%	$178.7179	$178.72	$178.70	$178.70
Purchase #2	$113.72	4.678%	$119.0398	$119.04	$119.05	$119.00
Purchase #3	$80.95	10.274%	$89.2668	$89.27	$89.25	$89.30
Purchase #4	$24.63	4.580%	$25.7581	$25.76	$25.75	$25.80
Purchase #5	$246.33	9.658%	$270.1206	$270.12	$270.10	$270.10
Purchase #6	$45.74	12.493%	$51.4543	$51.45	$51.45	$51.50
Purchase #7	$12.86	10.587%	$14.2215	$14.22	$14.20	$14.20
7 purchase totals =	$691.63		$748.5790	$748.58	$748.50	$748.60