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	$34.93	8.459%	$37.8847	$37.88	$37.90	$37.90
Purchase #2	$245.84	5.709%	$259.875	$259.88	$259.90	$259.90
Purchase #3	$228.84	5.637%	$241.7397	$241.74	$241.75	$241.70
Purchase #4	$228.43	8.308%	$247.408	$247.41	$247.40	$247.40
Purchase #5	$34.85	9.200%	$38.0562	$38.06	$38.05	$38.10
Purchase #6	$70.64	3.204%	$72.9033	$72.90	$72.90	$72.90
Purchase #7	$78.66	5.131%	$82.696	$82.70	$82.70	$82.70
7 purchase totals =	$922.19		$980.5629	$980.57	$980.60	$980.60