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	$16.72	12.613%	$18.8289	$18.83	$18.85	$18.80
Purchase #2	$40.91	3.113%	$42.1835	$42.18	$42.20	$42.20
Purchase #3	$54.57	10.375%	$60.2316	$60.23	$60.25	$60.20
Purchase #4	$58.57	4.664%	$61.3017	$61.30	$61.30	$61.30
Purchase #5	$166.61	9.676%	$182.7312	$182.73	$182.75	$182.70
Purchase #6	$38.94	9.724%	$42.7265	$42.73	$42.75	$42.70
Purchase #7	$64.45	7.793%	$69.4726	$69.47	$69.45	$69.50
7 purchase totals =	$440.77		$477.4760	$477.47	$477.55	$477.40