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	$21.83	11.826%	$24.4116	$24.41	$24.40	$24.40
Purchase #2	$182.26	4.471%	$190.4088	$190.41	$190.40	$190.40
Purchase #3	$110.35	12.298%	$123.9208	$123.92	$123.90	$123.90
Purchase #4	$58.98	3.236%	$60.8886	$60.89	$60.90	$60.90
Purchase #5	$209.47	11.290%	$233.1192	$233.12	$233.10	$233.10
Purchase #6	$180.69	9.361%	$197.6044	$197.60	$197.60	$197.60
Purchase #7	$234.27	7.492%	$251.8215	$251.82	$251.80	$251.80
7 purchase totals =	$997.85		$1,082.1749	$1,082.17	$1,082.10	$1,082.10