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	$18.88	13.135%	$21.3599	$21.36	$21.35	$21.40
Purchase #2	$164.94	13.756%	$187.6291	$187.63	$187.65	$187.60
Purchase #3	$159.32	8.162%	$172.3237	$172.32	$172.30	$172.30
Purchase #4	$147.31	4.543%	$154.0023	$154.00	$154.00	$154.00
Purchase #5	$240.55	12.156%	$269.7913	$269.79	$269.80	$269.80
Purchase #6	$148.49	9.534%	$162.647	$162.65	$162.65	$162.60
Purchase #7	$201.77	13.280%	$228.5651	$228.57	$228.55	$228.60
7 purchase totals =	$1,081.26		$1,196.3184	$1,196.32	$1,196.30	$1,196.30