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	$155.90	13.171%	$176.4336	$176.43	$176.45	$176.40
Purchase #2	$12.59	9.441%	$13.7786	$13.78	$13.80	$13.80
Purchase #3	$219.33	10.632%	$242.6492	$242.65	$242.65	$242.60
Purchase #4	$250.43	13.251%	$283.6145	$283.61	$283.60	$283.60
Purchase #5	$89.25	11.730%	$99.719	$99.72	$99.70	$99.70
Purchase #6	$40.47	8.589%	$43.946	$43.95	$43.95	$43.90
Purchase #7	$111.36	7.808%	$120.055	$120.06	$120.05	$120.10
7 purchase totals =	$879.33		$980.1959	$980.20	$980.20	$980.10