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	$213.47	12.384%	$239.9061	$239.91	$239.90	$239.90
Purchase #2	$128.82	5.447%	$135.8368	$135.84	$135.85	$135.80
Purchase #3	$81.61	10.535%	$90.2076	$90.21	$90.20	$90.20
Purchase #4	$189.64	5.213%	$199.5259	$199.53	$199.55	$199.50
Purchase #5	$22.50	4.780%	$23.5755	$23.58	$23.60	$23.60
Purchase #6	$106.34	4.640%	$111.2742	$111.27	$111.25	$111.30
Purchase #7	$37.34	10.815%	$41.3783	$41.38	$41.40	$41.40
7 purchase totals =	$779.72		$841.7044	$841.72	$841.75	$841.70