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	$239.60	8.150%	$259.1274	$259.13	$259.15	$259.10
Purchase #2	$99.42	4.204%	$103.5996	$103.60	$103.60	$103.60
Purchase #3	$47.26	10.268%	$52.1127	$52.11	$52.10	$52.10
Purchase #4	$77.47	6.326%	$82.3708	$82.37	$82.35	$82.40
Purchase #5	$165.55	10.355%	$182.6927	$182.69	$182.70	$182.70
Purchase #6	$73.37	7.327%	$78.7458	$78.75	$78.75	$78.70
Purchase #7	$191.34	13.389%	$216.9585	$216.96	$216.95	$217.00
7 purchase totals =	$894.01		$975.6075	$975.61	$975.60	$975.60