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	$84.98	6.104%	$90.1672	$90.17	$90.15	$90.20
Purchase #2	$161.30	4.647%	$168.7956	$168.80	$168.80	$168.80
Purchase #3	$183.73	13.673%	$208.8514	$208.85	$208.85	$208.90
Purchase #4	$54.64	12.783%	$61.6246	$61.62	$61.60	$61.60
Purchase #5	$19.31	5.522%	$20.3763	$20.38	$20.40	$20.40
Purchase #6	$169.32	11.663%	$189.0678	$189.07	$189.05	$189.10
Purchase #7	$233.27	11.658%	$260.4646	$260.46	$260.45	$260.50
7 purchase totals =	$906.55		$999.3475	$999.35	$999.30	$999.50