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	$149.59	3.251%	$154.4532	$154.45	$154.45	$154.50
Purchase #2	$171.59	6.531%	$182.7965	$182.80	$182.80	$182.80
Purchase #3	$27.54	8.256%	$29.8137	$29.81	$29.80	$29.80
Purchase #4	$37.59	7.311%	$40.3382	$40.34	$40.35	$40.30
Purchase #5	$98.40	7.488%	$105.7682	$105.77	$105.75	$105.80
Purchase #6	$53.85	13.685%	$61.2194	$61.22	$61.20	$61.20
Purchase #7	$59.82	7.718%	$64.4369	$64.44	$64.45	$64.40
7 purchase totals =	$598.38		$638.8261	$638.83	$638.80	$638.80