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	$35.77	13.763%	$40.693	$40.69	$40.70	$40.70
Purchase #2	$209.92	13.451%	$238.1563	$238.16	$238.15	$238.20
Purchase #3	$223.36	12.296%	$250.8243	$250.82	$250.80	$250.80
Purchase #4	$34.52	11.601%	$38.5247	$38.52	$38.50	$38.50
Purchase #5	$86.60	3.576%	$89.6968	$89.70	$89.70	$89.70
Purchase #6	$91.62	7.436%	$98.4329	$98.43	$98.45	$98.40
Purchase #7	$52.65	3.349%	$54.4132	$54.41	$54.40	$54.40
7 purchase totals =	$734.44		$810.7412	$810.73	$810.70	$810.70