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	$247.81	13.143%	$280.3797	$280.38	$280.40	$280.40
Purchase #2	$197.58	6.195%	$209.8201	$209.82	$209.80	$209.80
Purchase #3	$12.54	9.490%	$13.73	$13.73	$13.75	$13.70
Purchase #4	$76.32	3.474%	$78.9714	$78.97	$78.95	$79.00
Purchase #5	$241.72	7.229%	$259.1939	$259.19	$259.20	$259.20
Purchase #6	$98.40	6.156%	$104.4575	$104.46	$104.45	$104.50
Purchase #7	$235.46	12.305%	$264.4334	$264.43	$264.45	$264.40
7 purchase totals =	$1,109.83		$1,210.9860	$1,210.98	$1,211.00	$1,211.00