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	$241.61	7.152%	$258.8899	$258.89	$258.90	$258.90
Purchase #2	$239.56	4.403%	$250.1078	$250.11	$250.10	$250.10
Purchase #3	$40.54	8.435%	$43.9595	$43.96	$43.95	$44.00
Purchase #4	$18.46	8.364%	$20.004	$20.00	$20.00	$20.00
Purchase #5	$219.40	9.622%	$240.5107	$240.51	$240.50	$240.50
Purchase #6	$86.30	11.593%	$96.3048	$96.30	$96.30	$96.30
Purchase #7	$123.35	5.809%	$130.5154	$130.52	$130.50	$130.50
7 purchase totals =	$969.22		$1,040.2921	$1,040.29	$1,040.25	$1,040.30