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	$55.88	4.708%	$58.5108	$58.51	$58.50	$58.50
Purchase #2	$129.47	4.203%	$134.9116	$134.91	$134.90	$134.90
Purchase #3	$103.73	8.860%	$112.9205	$112.92	$112.90	$112.90
Purchase #4	$165.91	9.482%	$181.6416	$181.64	$181.65	$181.60
Purchase #5	$199.83	7.333%	$214.4835	$214.48	$214.50	$214.50
Purchase #6	$70.82	11.348%	$78.8567	$78.86	$78.85	$78.90
Purchase #7	$250.79	6.577%	$267.2845	$267.28	$267.30	$267.30
7 purchase totals =	$976.43		$1,048.6092	$1,048.60	$1,048.60	$1,048.60