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	$69.55	13.673%	$79.0596	$79.06	$79.05	$79.10
Purchase #2	$18.77	9.370%	$20.5287	$20.53	$20.55	$20.50
Purchase #3	$143.54	10.213%	$158.1997	$158.20	$158.20	$158.20
Purchase #4	$249.34	12.520%	$280.5574	$280.56	$280.55	$280.60
Purchase #5	$48.88	9.369%	$53.4596	$53.46	$53.45	$53.50
Purchase #6	$7.26	7.784%	$7.8251	$7.83	$7.85	$7.80
Purchase #7	$71.55	9.781%	$78.5483	$78.55	$78.55	$78.50
7 purchase totals =	$608.89		$678.1784	$678.19	$678.20	$678.20