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	$49.61	10.694%	$54.9153	$54.92	$54.90	$54.90
Purchase #2	$41.68	10.104%	$45.8913	$45.89	$45.90	$45.90
Purchase #3	$39.58	12.159%	$44.3925	$44.39	$44.40	$44.40
Purchase #4	$228.90	9.446%	$250.5219	$250.52	$250.50	$250.50
Purchase #5	$201.86	11.710%	$225.4978	$225.50	$225.50	$225.50
Purchase #6	$197.96	9.733%	$217.2274	$217.23	$217.25	$217.20
Purchase #7	$144.37	12.604%	$162.5664	$162.57	$162.55	$162.60
7 purchase totals =	$903.96		$1,001.0126	$1,001.02	$1,001.00	$1,001.00