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	$52.54	9.514%	$57.5387	$57.54	$57.55	$57.50
Purchase #2	$135.48	6.791%	$144.6804	$144.68	$144.70	$144.70
Purchase #3	$146.30	12.258%	$164.2335	$164.23	$164.25	$164.20
Purchase #4	$77.41	6.643%	$82.5523	$82.55	$82.55	$82.60
Purchase #5	$178.49	7.240%	$191.4127	$191.41	$191.40	$191.40
Purchase #6	$12.41	3.519%	$12.8467	$12.85	$12.85	$12.80
Purchase #7	$179.76	11.666%	$200.7308	$200.73	$200.75	$200.70
7 purchase totals =	$782.39		$853.9951	$853.99	$854.05	$853.90