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	$212.58	13.135%	$240.5024	$240.50	$240.50	$240.50
Purchase #2	$173.96	7.740%	$187.4245	$187.42	$187.40	$187.40
Purchase #3	$85.85	11.734%	$95.9236	$95.92	$95.90	$95.90
Purchase #4	$176.97	4.168%	$184.3461	$184.35	$184.35	$184.30
Purchase #5	$137.46	13.649%	$156.2219	$156.22	$156.20	$156.20
Purchase #6	$164.43	11.247%	$182.9234	$182.92	$182.90	$182.90
Purchase #7	$162.42	11.705%	$181.4313	$181.43	$181.45	$181.40
7 purchase totals =	$1,113.67		$1,228.7732	$1,228.76	$1,228.70	$1,228.60