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	$131.54	9.233%	$143.6851	$143.69	$143.70	$143.70
Purchase #2	$81.63	4.182%	$85.0438	$85.04	$85.05	$85.00
Purchase #3	$235.45	3.284%	$243.1822	$243.18	$243.20	$243.20
Purchase #4	$160.59	13.660%	$182.5266	$182.53	$182.55	$182.50
Purchase #5	$179.35	4.608%	$187.6144	$187.61	$187.60	$187.60
Purchase #6	$219.88	13.314%	$249.1548	$249.15	$249.15	$249.20
Purchase #7	$169.89	6.702%	$181.276	$181.28	$181.30	$181.30
7 purchase totals =	$1,178.33		$1,272.4829	$1,272.48	$1,272.55	$1,272.50