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	$79.91	12.545%	$89.9347	$89.93	$89.95	$89.90
Purchase #2	$93.88	11.293%	$104.4819	$104.48	$104.50	$104.50
Purchase #3	$41.68	4.747%	$43.6585	$43.66	$43.65	$43.70
Purchase #4	$224.98	12.666%	$253.476	$253.48	$253.50	$253.50
Purchase #5	$129.56	5.271%	$136.3891	$136.39	$136.40	$136.40
Purchase #6	$127.51	8.469%	$138.3088	$138.31	$138.30	$138.30
Purchase #7	$147.95	13.599%	$168.0697	$168.07	$168.05	$168.10
7 purchase totals =	$845.47		$934.3187	$934.32	$934.35	$934.40