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	$22.82	4.661%	$23.8836	$23.88	$23.90	$23.90
Purchase #2	$107.67	6.438%	$114.6018	$114.60	$114.60	$114.60
Purchase #3	$63.59	10.750%	$70.4259	$70.43	$70.45	$70.40
Purchase #4	$126.71	7.578%	$136.3121	$136.31	$136.30	$136.30
Purchase #5	$85.39	3.233%	$88.1507	$88.15	$88.15	$88.20
Purchase #6	$134.55	5.778%	$142.3243	$142.32	$142.30	$142.30
Purchase #7	$67.27	7.838%	$72.5426	$72.54	$72.55	$72.50
7 purchase totals =	$608.00		$648.2410	$648.23	$648.25	$648.20