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	$121.48	13.158%	$137.4643	$137.46	$137.45	$137.50
Purchase #2	$60.42	12.143%	$67.7568	$67.76	$67.75	$67.80
Purchase #3	$214.59	3.175%	$221.4032	$221.40	$221.40	$221.40
Purchase #4	$109.58	7.255%	$117.53	$117.53	$117.55	$117.50
Purchase #5	$91.37	3.202%	$94.2957	$94.30	$94.30	$94.30
Purchase #6	$170.65	6.562%	$181.8481	$181.85	$181.85	$181.80
Purchase #7	$195.54	13.265%	$221.4784	$221.48	$221.50	$221.50
7 purchase totals =	$963.63		$1,041.7765	$1,041.78	$1,041.80	$1,041.80