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	$63.76	10.399%	$70.3904	$70.39	$70.40	$70.40
Purchase #2	$10.78	11.147%	$11.9816	$11.98	$12.00	$12.00
Purchase #3	$124.97	7.675%	$134.5614	$134.56	$134.55	$134.60
Purchase #4	$100.45	13.333%	$113.843	$113.84	$113.85	$113.80
Purchase #5	$119.30	7.253%	$127.9528	$127.95	$127.95	$128.00
Purchase #6	$101.27	12.310%	$113.7363	$113.74	$113.75	$113.70
Purchase #7	$72.78	13.675%	$82.7327	$82.73	$82.75	$82.70
7 purchase totals =	$593.31		$655.1982	$655.19	$655.25	$655.20