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	$144.30	6.787%	$154.0936	$154.09	$154.10	$154.10
Purchase #2	$229.96	4.428%	$240.1426	$240.14	$240.15	$240.10
Purchase #3	$55.70	6.483%	$59.311	$59.31	$59.30	$59.30
Purchase #4	$214.39	4.379%	$223.7781	$223.78	$223.80	$223.80
Purchase #5	$243.81	4.400%	$254.5376	$254.54	$254.55	$254.50
Purchase #6	$131.65	6.291%	$139.9321	$139.93	$139.95	$139.90
Purchase #7	$214.95	11.261%	$239.1555	$239.16	$239.15	$239.20
7 purchase totals =	$1,234.76		$1,310.9505	$1,310.95	$1,311.00	$1,310.90