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	$188.60	4.170%	$196.4646	$196.46	$196.45	$196.50
Purchase #2	$196.40	4.655%	$205.5424	$205.54	$205.55	$205.50
Purchase #3	$54.97	9.849%	$60.384	$60.38	$60.40	$60.40
Purchase #4	$15.69	13.837%	$17.861	$17.86	$17.85	$17.90
Purchase #5	$85.33	10.873%	$94.6079	$94.61	$94.60	$94.60
Purchase #6	$125.90	3.630%	$130.4702	$130.47	$130.45	$130.50
Purchase #7	$119.42	12.816%	$134.7249	$134.72	$134.70	$134.70
7 purchase totals =	$786.31		$840.0550	$840.04	$840.00	$840.10