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	$80.55	10.719%	$89.1842	$89.18	$89.20	$89.20
Purchase #2	$201.45	8.714%	$219.0044	$219.00	$219.00	$219.00
Purchase #3	$114.60	13.808%	$130.424	$130.42	$130.40	$130.40
Purchase #4	$134.95	9.322%	$147.53	$147.53	$147.55	$147.50
Purchase #5	$54.90	11.835%	$61.3974	$61.40	$61.40	$61.40
Purchase #6	$40.31	6.243%	$42.8266	$42.83	$42.85	$42.80
Purchase #7	$224.54	4.808%	$235.3359	$235.34	$235.35	$235.30
7 purchase totals =	$851.30		$925.7025	$925.70	$925.75	$925.60