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	$246.28	11.671%	$275.0233	$275.02	$275.00	$275.00
Purchase #2	$145.60	3.654%	$150.9202	$150.92	$150.90	$150.90
Purchase #3	$179.64	13.733%	$204.31	$204.31	$204.30	$204.30
Purchase #4	$30.51	9.499%	$33.4081	$33.41	$33.40	$33.40
Purchase #5	$196.84	13.870%	$224.1417	$224.14	$224.15	$224.10
Purchase #6	$38.79	5.426%	$40.8947	$40.89	$40.90	$40.90
Purchase #7	$220.43	12.452%	$247.8779	$247.88	$247.90	$247.90
7 purchase totals =	$1,058.09		$1,176.5759	$1,176.57	$1,176.55	$1,176.50