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	$166.58	4.380%	$173.8762	$173.88	$173.90	$173.90
Purchase #2	$117.62	11.660%	$131.3345	$131.33	$131.35	$131.30
Purchase #3	$149.50	11.370%	$166.4982	$166.50	$166.50	$166.50
Purchase #4	$24.78	9.524%	$27.14	$27.14	$27.15	$27.10
Purchase #5	$125.90	13.759%	$143.2226	$143.22	$143.20	$143.20
Purchase #6	$191.86	7.587%	$206.4164	$206.42	$206.40	$206.40
Purchase #7	$67.42	13.527%	$76.5399	$76.54	$76.55	$76.50
7 purchase totals =	$843.66		$925.0278	$925.03	$925.05	$924.90