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	$171.85	4.123%	$178.9354	$178.94	$178.95	$178.90
Purchase #2	$155.54	3.710%	$161.3105	$161.31	$161.30	$161.30
Purchase #3	$228.61	5.736%	$241.7231	$241.72	$241.70	$241.70
Purchase #4	$220.74	12.450%	$248.2221	$248.22	$248.20	$248.20
Purchase #5	$180.89	8.607%	$196.4592	$196.46	$196.45	$196.50
Purchase #6	$228.59	5.677%	$241.5671	$241.57	$241.55	$241.60
Purchase #7	$130.80	13.371%	$148.2893	$148.29	$148.30	$148.30
7 purchase totals =	$1,317.02		$1,416.5067	$1,416.51	$1,416.45	$1,416.50