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	$126.34	4.337%	$131.8194	$131.82	$131.80	$131.80
Purchase #2	$202.55	13.777%	$230.4553	$230.46	$230.45	$230.50
Purchase #3	$163.37	5.214%	$171.8881	$171.89	$171.90	$171.90
Purchase #4	$32.55	4.236%	$33.9288	$33.93	$33.95	$33.90
Purchase #5	$126.42	12.158%	$141.7901	$141.79	$141.80	$141.80
Purchase #6	$109.59	5.628%	$115.7577	$115.76	$115.75	$115.80
Purchase #7	$13.26	4.313%	$13.8319	$13.83	$13.85	$13.80
7 purchase totals =	$774.08		$839.4713	$839.48	$839.50	$839.50