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	$127.33	7.179%	$136.471	$136.47	$136.45	$136.50
Purchase #2	$123.69	12.105%	$138.6627	$138.66	$138.65	$138.70
Purchase #3	$104.49	4.410%	$109.098	$109.10	$109.10	$109.10
Purchase #4	$250.75	12.155%	$281.2287	$281.23	$281.25	$281.20
Purchase #5	$226.43	6.537%	$241.2317	$241.23	$241.25	$241.20
Purchase #6	$74.54	8.521%	$80.8916	$80.89	$80.90	$80.90
Purchase #7	$24.44	12.660%	$27.5341	$27.53	$27.55	$27.50
7 purchase totals =	$931.67		$1,015.1178	$1,015.11	$1,015.15	$1,015.10