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	$150.38	10.227%	$165.7594	$165.76	$165.75	$165.80
Purchase #2	$123.27	4.181%	$128.4239	$128.42	$128.40	$128.40
Purchase #3	$147.61	11.412%	$164.4553	$164.46	$164.45	$164.50
Purchase #4	$73.82	4.715%	$77.3006	$77.30	$77.30	$77.30
Purchase #5	$105.73	5.397%	$111.4362	$111.44	$111.45	$111.40
Purchase #6	$91.71	5.807%	$97.0356	$97.04	$97.05	$97.00
Purchase #7	$219.33	9.245%	$239.6071	$239.61	$239.60	$239.60
7 purchase totals =	$911.85		$984.0181	$984.03	$984.00	$984.00