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	$94.93	3.845%	$98.5801	$98.58	$98.60	$98.60
Purchase #2	$38.81	4.691%	$40.6306	$40.63	$40.65	$40.60
Purchase #3	$134.81	10.530%	$149.0055	$149.01	$149.00	$149.00
Purchase #4	$35.76	9.342%	$39.1007	$39.10	$39.10	$39.10
Purchase #5	$99.63	10.229%	$109.8212	$109.82	$109.80	$109.80
Purchase #6	$146.50	6.809%	$156.4752	$156.48	$156.50	$156.50
Purchase #7	$212.28	10.449%	$234.4611	$234.46	$234.45	$234.50
7 purchase totals =	$762.72		$828.0744	$828.08	$828.10	$828.10