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	$123.35	10.651%	$136.488	$136.49	$136.50	$136.50
Purchase #2	$129.90	13.825%	$147.8587	$147.86	$147.85	$147.90
Purchase #3	$191.28	10.370%	$211.1157	$211.12	$211.10	$211.10
Purchase #4	$52.50	7.710%	$56.5478	$56.55	$56.55	$56.50
Purchase #5	$43.86	7.777%	$47.271	$47.27	$47.25	$47.30
Purchase #6	$153.34	12.311%	$172.2177	$172.22	$172.20	$172.20
Purchase #7	$224.43	5.374%	$236.4909	$236.49	$236.50	$236.50
7 purchase totals =	$918.66		$1,007.9898	$1,008.00	$1,007.95	$1,008.00