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	$28.46	10.299%	$31.3911	$31.39	$31.40	$31.40
Purchase #2	$141.65	10.194%	$156.0898	$156.09	$156.10	$156.10
Purchase #3	$114.33	4.453%	$119.4211	$119.42	$119.40	$119.40
Purchase #4	$109.63	4.770%	$114.8594	$114.86	$114.85	$114.90
Purchase #5	$152.31	13.387%	$172.6997	$172.70	$172.70	$172.70
Purchase #6	$48.33	6.552%	$51.4966	$51.50	$51.50	$51.50
Purchase #7	$61.74	13.782%	$70.249	$70.25	$70.25	$70.20
7 purchase totals =	$656.45		$716.2067	$716.21	$716.20	$716.20