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	$61.28	4.570%	$64.0805	$64.08	$64.10	$64.10
Purchase #2	$206.72	7.305%	$221.8209	$221.82	$221.80	$221.80
Purchase #3	$235.91	10.439%	$260.5366	$260.54	$260.55	$260.50
Purchase #4	$178.66	11.772%	$199.6919	$199.69	$199.70	$199.70
Purchase #5	$80.76	10.609%	$89.3278	$89.33	$89.35	$89.30
Purchase #6	$25.65	12.783%	$28.9288	$28.93	$28.95	$28.90
Purchase #7	$137.46	11.273%	$152.9559	$152.96	$152.95	$153.00
7 purchase totals =	$926.44		$1,017.3424	$1,017.35	$1,017.40	$1,017.30