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	$150.57	13.489%	$170.8804	$170.88	$170.90	$170.90
Purchase #2	$178.52	4.773%	$187.0408	$187.04	$187.05	$187.00
Purchase #3	$36.82	13.221%	$41.688	$41.69	$41.70	$41.70
Purchase #4	$127.94	13.274%	$144.9228	$144.92	$144.90	$144.90
Purchase #5	$185.66	4.786%	$194.5457	$194.55	$194.55	$194.50
Purchase #6	$166.50	9.683%	$182.6222	$182.62	$182.60	$182.60
Purchase #7	$211.44	9.525%	$231.5797	$231.58	$231.60	$231.60
7 purchase totals =	$1,057.45		$1,153.2796	$1,153.28	$1,153.30	$1,153.20