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	$227.60	9.791%	$249.8843	$249.88	$249.90	$249.90
Purchase #2	$162.70	11.510%	$181.4268	$181.43	$181.45	$181.40
Purchase #3	$167.52	11.787%	$187.2656	$187.27	$187.25	$187.30
Purchase #4	$54.63	3.363%	$56.4672	$56.47	$56.45	$56.50
Purchase #5	$37.64	9.611%	$41.2576	$41.26	$41.25	$41.30
Purchase #6	$101.74	3.400%	$105.1992	$105.20	$105.20	$105.20
Purchase #7	$124.35	9.765%	$136.4928	$136.49	$136.50	$136.50
7 purchase totals =	$876.18		$957.9935	$958.00	$958.00	$958.10