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	$136.75	5.425%	$144.1687	$144.17	$144.15	$144.20
Purchase #2	$32.83	7.124%	$35.1688	$35.17	$35.15	$35.20
Purchase #3	$141.53	11.625%	$157.9829	$157.98	$158.00	$158.00
Purchase #4	$40.47	6.714%	$43.1872	$43.19	$43.20	$43.20
Purchase #5	$80.86	12.223%	$90.7435	$90.74	$90.75	$90.70
Purchase #6	$134.27	6.631%	$143.1734	$143.17	$143.15	$143.20
Purchase #7	$248.30	5.735%	$262.54	$262.54	$262.55	$262.50
7 purchase totals =	$815.01		$876.9645	$876.96	$876.95	$877.00