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	$161.94	5.533%	$170.9001	$170.90	$170.90	$170.90
Purchase #2	$155.92	12.698%	$175.7187	$175.72	$175.70	$175.70
Purchase #3	$249.50	7.601%	$268.4645	$268.46	$268.45	$268.50
Purchase #4	$178.90	3.427%	$185.0309	$185.03	$185.05	$185.00
Purchase #5	$148.94	4.631%	$155.8374	$155.84	$155.85	$155.80
Purchase #6	$100.54	8.410%	$108.9954	$109.00	$109.00	$109.00
Purchase #7	$243.58	5.343%	$256.5945	$256.59	$256.60	$256.60
7 purchase totals =	$1,239.32		$1,321.5415	$1,321.54	$1,321.55	$1,321.50