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	$103.63	4.236%	$108.0198	$108.02	$108.00	$108.00
Purchase #2	$140.94	9.608%	$154.4815	$154.48	$154.50	$154.50
Purchase #3	$39.63	7.409%	$42.5662	$42.57	$42.55	$42.60
Purchase #4	$90.42	6.385%	$96.1933	$96.19	$96.20	$96.20
Purchase #5	$209.97	13.526%	$238.3705	$238.37	$238.35	$238.40
Purchase #6	$108.59	10.522%	$120.0158	$120.02	$120.00	$120.00
Purchase #7	$18.76	9.111%	$20.4692	$20.47	$20.45	$20.50
7 purchase totals =	$711.94		$780.1163	$780.12	$780.05	$780.20