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	$51.28	8.345%	$55.5593	$55.56	$55.55	$55.60
Purchase #2	$247.37	13.308%	$280.29	$280.29	$280.30	$280.30
Purchase #3	$124.91	5.302%	$131.5327	$131.53	$131.55	$131.50
Purchase #4	$131.54	9.800%	$144.4309	$144.43	$144.45	$144.40
Purchase #5	$64.88	11.653%	$72.4405	$72.44	$72.45	$72.40
Purchase #6	$68.52	6.623%	$73.0581	$73.06	$73.05	$73.10
Purchase #7	$103.74	6.536%	$110.5204	$110.52	$110.50	$110.50
7 purchase totals =	$792.24		$867.8319	$867.83	$867.85	$867.80