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	$245.84	12.104%	$275.5965	$275.60	$275.60	$275.60
Purchase #2	$72.25	7.805%	$77.8891	$77.89	$77.90	$77.90
Purchase #3	$171.90	4.404%	$179.4705	$179.47	$179.45	$179.50
Purchase #4	$21.84	7.498%	$23.4776	$23.48	$23.50	$23.50
Purchase #5	$52.32	3.109%	$53.9466	$53.95	$53.95	$53.90
Purchase #6	$211.90	10.273%	$233.6685	$233.67	$233.65	$233.70
Purchase #7	$170.46	8.153%	$184.3576	$184.36	$184.35	$184.40
7 purchase totals =	$946.51		$1,028.4064	$1,028.42	$1,028.40	$1,028.50