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	$84.54	10.200%	$93.1631	$93.16	$93.15	$93.20
Purchase #2	$155.95	6.863%	$166.6528	$166.65	$166.65	$166.70
Purchase #3	$113.41	12.616%	$127.7178	$127.72	$127.70	$127.70
Purchase #4	$97.27	7.441%	$104.5079	$104.51	$104.50	$104.50
Purchase #5	$114.84	11.220%	$127.725	$127.73	$127.75	$127.70
Purchase #6	$193.70	3.598%	$200.6693	$200.67	$200.65	$200.70
Purchase #7	$103.62	5.850%	$109.6818	$109.68	$109.70	$109.70
7 purchase totals =	$863.33		$930.1177	$930.12	$930.10	$930.20