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	$112.92	6.394%	$120.1401	$120.14	$120.15	$120.10
Purchase #2	$161.40	3.175%	$166.5245	$166.52	$166.50	$166.50
Purchase #3	$44.62	9.490%	$48.8544	$48.85	$48.85	$48.90
Purchase #4	$138.61	3.751%	$143.8093	$143.81	$143.80	$143.80
Purchase #5	$146.69	12.719%	$165.3475	$165.35	$165.35	$165.30
Purchase #6	$168.28	10.430%	$185.8316	$185.83	$185.85	$185.80
Purchase #7	$199.72	6.842%	$213.3848	$213.38	$213.40	$213.40
7 purchase totals =	$972.24		$1,043.8922	$1,043.88	$1,043.90	$1,043.80