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	$155.94	6.828%	$166.5876	$166.59	$166.60	$166.60
Purchase #2	$66.50	7.142%	$71.2494	$71.25	$71.25	$71.20
Purchase #3	$138.67	6.239%	$147.3216	$147.32	$147.30	$147.30
Purchase #4	$174.95	5.465%	$184.511	$184.51	$184.50	$184.50
Purchase #5	$217.46	5.357%	$229.1093	$229.11	$229.10	$229.10
Purchase #6	$35.34	11.259%	$39.3189	$39.32	$39.30	$39.30
Purchase #7	$89.99	9.352%	$98.4059	$98.41	$98.40	$98.40
7 purchase totals =	$878.85		$936.5037	$936.51	$936.45	$936.40