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	$138.34	8.801%	$150.5153	$150.52	$150.50	$150.50
Purchase #2	$109.25	10.641%	$120.8753	$120.88	$120.90	$120.90
Purchase #3	$28.28	6.294%	$30.0599	$30.06	$30.05	$30.10
Purchase #4	$223.88	10.518%	$247.4277	$247.43	$247.45	$247.40
Purchase #5	$103.37	8.376%	$112.0283	$112.03	$112.05	$112.00
Purchase #6	$58.30	6.745%	$62.2323	$62.23	$62.25	$62.20
Purchase #7	$73.32	12.140%	$82.221	$82.22	$82.20	$82.20
7 purchase totals =	$734.74		$805.3598	$805.37	$805.40	$805.30