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	$111.59	7.352%	$119.7941	$119.79	$119.80	$119.80
Purchase #2	$52.57	3.557%	$54.4399	$54.44	$54.45	$54.40
Purchase #3	$231.50	8.665%	$251.5595	$251.56	$251.55	$251.60
Purchase #4	$186.63	12.594%	$210.1342	$210.13	$210.15	$210.10
Purchase #5	$178.37	12.302%	$200.3131	$200.31	$200.30	$200.30
Purchase #6	$36.25	12.156%	$40.6566	$40.66	$40.65	$40.70
Purchase #7	$29.75	10.684%	$32.9285	$32.93	$32.95	$32.90
7 purchase totals =	$826.66		$909.8259	$909.82	$909.85	$909.80