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	$25.56	10.767%	$28.312	$28.31	$28.30	$28.30
Purchase #2	$116.86	6.622%	$124.5985	$124.60	$124.60	$124.60
Purchase #3	$66.63	9.707%	$73.0978	$73.10	$73.10	$73.10
Purchase #4	$127.90	12.872%	$144.3633	$144.36	$144.35	$144.40
Purchase #5	$123.94	10.842%	$137.3776	$137.38	$137.40	$137.40
Purchase #6	$150.45	5.279%	$158.3923	$158.39	$158.40	$158.40
Purchase #7	$42.56	7.570%	$45.7818	$45.78	$45.80	$45.80
7 purchase totals =	$653.90		$711.9233	$711.92	$711.95	$712.00