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	$150.66	12.456%	$169.4262	$169.43	$169.45	$169.40
Purchase #2	$58.43	6.325%	$62.1257	$62.13	$62.15	$62.10
Purchase #3	$158.91	7.582%	$170.9586	$170.96	$170.95	$171.00
Purchase #4	$212.96	11.606%	$237.6761	$237.68	$237.70	$237.70
Purchase #5	$234.49	9.122%	$255.8802	$255.88	$255.90	$255.90
Purchase #6	$60.40	3.196%	$62.3304	$62.33	$62.35	$62.30
Purchase #7	$41.32	6.428%	$43.976	$43.98	$44.00	$44.00
7 purchase totals =	$917.17		$1,002.3732	$1,002.39	$1,002.50	$1,002.40