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	$238.46	11.640%	$266.2167	$266.22	$266.20	$266.20
Purchase #2	$146.78	6.578%	$156.4352	$156.44	$156.45	$156.40
Purchase #3	$178.77	7.176%	$191.5985	$191.60	$191.60	$191.60
Purchase #4	$226.68	3.471%	$234.5481	$234.55	$234.55	$234.50
Purchase #5	$219.97	13.428%	$249.5076	$249.51	$249.50	$249.50
Purchase #6	$37.75	13.515%	$42.8519	$42.85	$42.85	$42.90
Purchase #7	$211.45	12.696%	$238.2957	$238.30	$238.30	$238.30
7 purchase totals =	$1,259.86		$1,379.4537	$1,379.47	$1,379.45	$1,379.40