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	$33.34	12.611%	$37.5445	$37.54	$37.55	$37.50
Purchase #2	$123.51	12.630%	$139.1093	$139.11	$139.10	$139.10
Purchase #3	$225.97	5.195%	$237.7091	$237.71	$237.70	$237.70
Purchase #4	$7.77	4.823%	$8.1447	$8.14	$8.15	$8.10
Purchase #5	$62.55	3.395%	$64.6736	$64.67	$64.65	$64.70
Purchase #6	$80.39	3.117%	$82.8958	$82.90	$82.90	$82.90
Purchase #7	$28.72	12.431%	$32.2902	$32.29	$32.30	$32.30
7 purchase totals =	$562.25		$602.3672	$602.36	$602.35	$602.30