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	$81.58	10.238%	$89.9322	$89.93	$89.95	$89.90
Purchase #2	$100.77	9.458%	$110.3008	$110.30	$110.30	$110.30
Purchase #3	$51.50	7.637%	$55.4331	$55.43	$55.45	$55.40
Purchase #4	$115.62	11.537%	$128.9591	$128.96	$128.95	$129.00
Purchase #5	$34.72	11.738%	$38.7954	$38.80	$38.80	$38.80
Purchase #6	$101.47	7.846%	$109.4313	$109.43	$109.45	$109.40
Purchase #7	$33.62	11.695%	$37.5519	$37.55	$37.55	$37.60
7 purchase totals =	$519.28		$570.4038	$570.40	$570.45	$570.40