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	$171.93	6.563%	$183.2138	$183.21	$183.20	$183.20
Purchase #2	$40.47	3.692%	$41.9642	$41.96	$41.95	$42.00
Purchase #3	$77.88	7.240%	$83.5185	$83.52	$83.50	$83.50
Purchase #4	$29.56	10.181%	$32.5695	$32.57	$32.55	$32.60
Purchase #5	$121.74	6.484%	$129.6336	$129.63	$129.65	$129.60
Purchase #6	$57.83	6.571%	$61.63	$61.63	$61.65	$61.60
Purchase #7	$111.34	11.255%	$123.8713	$123.87	$123.85	$123.90
7 purchase totals =	$610.75		$656.4009	$656.39	$656.35	$656.40