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	$165.52	8.554%	$179.6786	$179.68	$179.70	$179.70
Purchase #2	$144.57	3.813%	$150.0825	$150.08	$150.10	$150.10
Purchase #3	$250.87	9.444%	$274.5622	$274.56	$274.55	$274.60
Purchase #4	$148.31	11.676%	$165.6267	$165.63	$165.65	$165.60
Purchase #5	$126.72	4.499%	$132.4211	$132.42	$132.40	$132.40
Purchase #6	$14.68	8.457%	$15.9215	$15.92	$15.90	$15.90
Purchase #7	$196.29	6.487%	$209.0233	$209.02	$209.00	$209.00
7 purchase totals =	$1,046.96		$1,127.3159	$1,127.31	$1,127.30	$1,127.30