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	$83.80	6.326%	$89.1012	$89.10	$89.10	$89.10
Purchase #2	$138.45	4.362%	$144.4892	$144.49	$144.50	$144.50
Purchase #3	$176.56	5.714%	$186.6486	$186.65	$186.65	$186.60
Purchase #4	$177.87	7.566%	$191.3276	$191.33	$191.35	$191.30
Purchase #5	$48.91	11.155%	$54.3659	$54.37	$54.35	$54.40
Purchase #6	$79.26	7.629%	$85.3067	$85.31	$85.30	$85.30
Purchase #7	$158.75	5.282%	$167.1352	$167.14	$167.15	$167.10
7 purchase totals =	$863.60		$918.3744	$918.39	$918.40	$918.30