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	$118.89	4.626%	$124.3899	$124.39	$124.40	$124.40
Purchase #2	$91.44	12.714%	$103.0657	$103.07	$103.05	$103.10
Purchase #3	$21.91	11.499%	$24.4294	$24.43	$24.45	$24.40
Purchase #4	$80.47	3.288%	$83.1159	$83.12	$83.10	$83.10
Purchase #5	$57.86	6.722%	$61.7493	$61.75	$61.75	$61.70
Purchase #6	$134.51	12.220%	$150.9471	$150.95	$150.95	$150.90
Purchase #7	$60.30	3.529%	$62.428	$62.43	$62.45	$62.40
7 purchase totals =	$565.38		$610.1253	$610.14	$610.15	$610.00