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	$45.78	3.705%	$47.4761	$47.48	$47.50	$47.50
Purchase #2	$165.42	8.649%	$179.7272	$179.73	$179.75	$179.70
Purchase #3	$96.73	13.187%	$109.4858	$109.49	$109.50	$109.50
Purchase #4	$122.55	3.840%	$127.2559	$127.26	$127.25	$127.30
Purchase #5	$66.90	11.859%	$74.8337	$74.83	$74.85	$74.80
Purchase #6	$105.93	5.600%	$111.8621	$111.86	$111.85	$111.90
Purchase #7	$247.79	9.851%	$272.1998	$272.20	$272.20	$272.20
7 purchase totals =	$851.10		$922.8406	$922.85	$922.90	$922.90