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	$18.92	6.303%	$20.1125	$20.11	$20.10	$20.10
Purchase #2	$86.44	11.382%	$96.2786	$96.28	$96.30	$96.30
Purchase #3	$119.82	7.494%	$128.7993	$128.80	$128.80	$128.80
Purchase #4	$175.49	3.534%	$181.6918	$181.69	$181.70	$181.70
Purchase #5	$169.45	9.227%	$185.0852	$185.09	$185.10	$185.10
Purchase #6	$197.26	4.160%	$205.466	$205.47	$205.45	$205.50
Purchase #7	$41.51	3.174%	$42.8275	$42.83	$42.85	$42.80
7 purchase totals =	$808.89		$860.2609	$860.27	$860.30	$860.30