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	$85.49	3.827%	$88.7617	$88.76	$88.75	$88.80
Purchase #2	$50.65	7.593%	$54.4959	$54.50	$54.50	$54.50
Purchase #3	$153.31	7.183%	$164.3223	$164.32	$164.30	$164.30
Purchase #4	$167.46	8.757%	$182.1245	$182.12	$182.10	$182.10
Purchase #5	$119.49	3.787%	$124.0151	$124.02	$124.00	$124.00
Purchase #6	$132.43	5.637%	$139.8951	$139.90	$139.90	$139.90
Purchase #7	$200.33	13.583%	$227.5408	$227.54	$227.55	$227.50
7 purchase totals =	$909.16		$981.1554	$981.16	$981.10	$981.10