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	$227.36	12.366%	$255.4753	$255.48	$255.50	$255.50
Purchase #2	$146.47	4.848%	$153.5709	$153.57	$153.55	$153.60
Purchase #3	$199.70	10.580%	$220.8283	$220.83	$220.85	$220.80
Purchase #4	$233.34	7.344%	$250.4765	$250.48	$250.50	$250.50
Purchase #5	$119.93	9.399%	$131.2022	$131.20	$131.20	$131.20
Purchase #6	$33.95	12.132%	$38.0688	$38.07	$38.05	$38.10
Purchase #7	$141.98	6.218%	$150.8083	$150.81	$150.80	$150.80
7 purchase totals =	$1,102.73		$1,200.4303	$1,200.44	$1,200.45	$1,200.50