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	$73.85	9.435%	$80.8177	$80.82	$80.80	$80.80
Purchase #2	$56.48	8.182%	$61.1012	$61.10	$61.10	$61.10
Purchase #3	$91.52	7.202%	$98.1113	$98.11	$98.10	$98.10
Purchase #4	$72.32	8.623%	$78.5562	$78.56	$78.55	$78.60
Purchase #5	$118.70	10.396%	$131.0401	$131.04	$131.05	$131.00
Purchase #6	$246.95	7.750%	$266.0886	$266.09	$266.10	$266.10
Purchase #7	$66.68	9.532%	$73.0359	$73.04	$73.05	$73.00
7 purchase totals =	$726.50		$788.7510	$788.76	$788.75	$788.70