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	$27.91	11.568%	$31.1386	$31.14	$31.15	$31.10
Purchase #2	$183.90	6.632%	$196.0962	$196.10	$196.10	$196.10
Purchase #3	$225.33	6.608%	$240.2198	$240.22	$240.20	$240.20
Purchase #4	$75.63	11.565%	$84.3766	$84.38	$84.40	$84.40
Purchase #5	$189.51	13.592%	$215.2682	$215.27	$215.25	$215.30
Purchase #6	$108.32	4.128%	$112.7914	$112.79	$112.80	$112.80
Purchase #7	$49.77	13.345%	$56.4118	$56.41	$56.40	$56.40
7 purchase totals =	$860.37		$936.3026	$936.31	$936.30	$936.30