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	$229.86	3.733%	$238.4407	$238.44	$238.45	$238.40
Purchase #2	$245.88	5.792%	$260.1214	$260.12	$260.10	$260.10
Purchase #3	$84.88	13.194%	$96.0791	$96.08	$96.10	$96.10
Purchase #4	$55.72	6.226%	$59.1891	$59.19	$59.20	$59.20
Purchase #5	$73.73	11.326%	$82.0807	$82.08	$82.10	$82.10
Purchase #6	$97.36	4.153%	$101.4034	$101.40	$101.40	$101.40
Purchase #7	$232.84	12.799%	$262.6412	$262.64	$262.65	$262.60
7 purchase totals =	$1,020.27		$1,099.9556	$1,099.95	$1,100.00	$1,099.90