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	$50.56	7.768%	$54.4875	$54.49	$54.50	$54.50
Purchase #2	$173.33	9.804%	$190.3233	$190.32	$190.30	$190.30
Purchase #3	$7.39	8.754%	$8.0369	$8.04	$8.05	$8.00
Purchase #4	$104.51	6.612%	$111.4202	$111.42	$111.40	$111.40
Purchase #5	$21.69	8.150%	$23.4577	$23.46	$23.45	$23.50
Purchase #6	$208.49	9.666%	$228.6426	$228.64	$228.65	$228.60
Purchase #7	$67.83	6.385%	$72.1609	$72.16	$72.15	$72.20
7 purchase totals =	$633.80		$688.5291	$688.53	$688.50	$688.50