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	$231.70	5.109%	$243.5376	$243.54	$243.55	$243.50
Purchase #2	$99.66	11.862%	$111.4817	$111.48	$111.50	$111.50
Purchase #3	$92.76	13.349%	$105.1425	$105.14	$105.15	$105.10
Purchase #4	$152.31	8.366%	$165.0523	$165.05	$165.05	$165.10
Purchase #5	$150.54	12.422%	$169.2401	$169.24	$169.25	$169.20
Purchase #6	$47.39	5.799%	$50.1381	$50.14	$50.15	$50.10
Purchase #7	$138.80	12.719%	$156.454	$156.45	$156.45	$156.50
7 purchase totals =	$913.16		$1,001.0463	$1,001.04	$1,001.10	$1,001.00