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	$12.44	9.251%	$13.5908	$13.59	$13.60	$13.60
Purchase #2	$43.29	8.482%	$46.9619	$46.96	$46.95	$47.00
Purchase #3	$187.73	5.741%	$198.5076	$198.51	$198.50	$198.50
Purchase #4	$79.94	11.445%	$89.0891	$89.09	$89.10	$89.10
Purchase #5	$110.86	3.352%	$114.576	$114.58	$114.60	$114.60
Purchase #6	$57.56	12.842%	$64.9519	$64.95	$64.95	$65.00
Purchase #7	$124.82	13.463%	$141.6245	$141.62	$141.60	$141.60
7 purchase totals =	$616.64		$669.3018	$669.30	$669.30	$669.40