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	$122.79	6.688%	$131.0022	$131.00	$131.00	$131.00
Purchase #2	$240.27	4.534%	$251.1638	$251.16	$251.15	$251.20
Purchase #3	$181.37	4.696%	$189.8871	$189.89	$189.90	$189.90
Purchase #4	$192.83	12.637%	$217.1979	$217.20	$217.20	$217.20
Purchase #5	$104.39	9.610%	$114.4219	$114.42	$114.40	$114.40
Purchase #6	$17.49	7.391%	$18.7827	$18.78	$18.80	$18.80
Purchase #7	$97.72	3.261%	$100.9066	$100.91	$100.90	$100.90
7 purchase totals =	$956.86		$1,023.3622	$1,023.36	$1,023.35	$1,023.40