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	$181.74	10.332%	$200.5174	$200.52	$200.50	$200.50
Purchase #2	$135.31	3.774%	$140.4166	$140.42	$140.40	$140.40
Purchase #3	$87.50	3.786%	$90.8128	$90.81	$90.80	$90.80
Purchase #4	$72.51	9.828%	$79.6363	$79.64	$79.65	$79.60
Purchase #5	$172.52	7.112%	$184.7896	$184.79	$184.80	$184.80
Purchase #6	$248.26	13.413%	$281.5591	$281.56	$281.55	$281.60
Purchase #7	$105.62	3.501%	$109.3178	$109.32	$109.30	$109.30
7 purchase totals =	$1,003.46		$1,087.0496	$1,087.06	$1,087.00	$1,087.00