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	$116.35	4.357%	$121.4194	$121.42	$121.40	$121.40
Purchase #2	$179.65	9.305%	$196.3664	$196.37	$196.35	$196.40
Purchase #3	$78.85	6.380%	$83.8806	$83.88	$83.90	$83.90
Purchase #4	$62.38	6.478%	$66.421	$66.42	$66.40	$66.40
Purchase #5	$141.56	7.334%	$151.942	$151.94	$151.95	$151.90
Purchase #6	$185.32	11.597%	$206.8116	$206.81	$206.80	$206.80
Purchase #7	$91.71	6.680%	$97.8362	$97.84	$97.85	$97.80
7 purchase totals =	$855.82		$924.6772	$924.68	$924.65	$924.60