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	$204.29	12.819%	$230.4779	$230.48	$230.50	$230.50
Purchase #2	$64.35	7.608%	$69.2457	$69.25	$69.25	$69.20
Purchase #3	$202.31	6.583%	$215.6281	$215.63	$215.65	$215.60
Purchase #4	$185.30	8.441%	$200.9412	$200.94	$200.95	$200.90
Purchase #5	$240.51	8.315%	$260.5084	$260.51	$260.50	$260.50
Purchase #6	$126.27	12.756%	$142.377	$142.38	$142.40	$142.40
Purchase #7	$130.72	4.282%	$136.3174	$136.32	$136.30	$136.30
7 purchase totals =	$1,153.75		$1,255.4957	$1,255.51	$1,255.55	$1,255.40