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	$120.42	5.784%	$127.3851	$127.39	$127.40	$127.40
Purchase #2	$197.82	11.675%	$220.9155	$220.92	$220.90	$220.90
Purchase #3	$55.33	5.845%	$58.564	$58.56	$58.55	$58.60
Purchase #4	$77.63	11.788%	$86.781	$86.78	$86.80	$86.80
Purchase #5	$36.80	5.868%	$38.9594	$38.96	$38.95	$39.00
Purchase #6	$144.51	11.700%	$161.4177	$161.42	$161.40	$161.40
Purchase #7	$226.98	12.650%	$255.693	$255.69	$255.70	$255.70
7 purchase totals =	$859.49		$949.7157	$949.72	$949.70	$949.80