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	$6.64	5.489%	$7.0045	$7.00	$7.00	$7.00
Purchase #2	$60.28	12.310%	$67.7005	$67.70	$67.70	$67.70
Purchase #3	$78.63	5.179%	$82.7022	$82.70	$82.70	$82.70
Purchase #4	$11.25	10.129%	$12.3895	$12.39	$12.40	$12.40
Purchase #5	$151.72	8.756%	$165.0046	$165.00	$165.00	$165.00
Purchase #6	$128.51	10.760%	$142.3377	$142.34	$142.35	$142.30
Purchase #7	$131.40	9.483%	$143.8607	$143.86	$143.85	$143.90
7 purchase totals =	$568.43		$620.9997	$620.99	$621.00	$621.00