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	$39.39	7.668%	$42.4104	$42.41	$42.40	$42.40
Purchase #2	$229.66	9.328%	$251.0827	$251.08	$251.10	$251.10
Purchase #3	$186.62	5.147%	$196.2253	$196.23	$196.25	$196.20
Purchase #4	$155.81	6.321%	$165.6588	$165.66	$165.65	$165.70
Purchase #5	$110.89	5.227%	$116.6862	$116.69	$116.70	$116.70
Purchase #6	$224.76	5.314%	$236.7037	$236.70	$236.70	$236.70
Purchase #7	$248.63	12.680%	$280.1563	$280.16	$280.15	$280.20
7 purchase totals =	$1,195.76		$1,288.9234	$1,288.93	$1,288.95	$1,289.00