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	$80.39	11.393%	$89.5488	$89.55	$89.55	$89.50
Purchase #2	$35.94	6.741%	$38.3627	$38.36	$38.35	$38.40
Purchase #3	$244.90	10.220%	$269.9288	$269.93	$269.95	$269.90
Purchase #4	$39.91	5.850%	$42.2447	$42.24	$42.25	$42.20
Purchase #5	$194.42	13.509%	$220.6842	$220.68	$220.70	$220.70
Purchase #6	$142.67	10.621%	$157.823	$157.82	$157.80	$157.80
Purchase #7	$181.88	10.431%	$200.8519	$200.85	$200.85	$200.90
7 purchase totals =	$920.11		$1,019.4441	$1,019.43	$1,019.45	$1,019.40