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	$240.62	12.270%	$270.1441	$270.14	$270.15	$270.10
Purchase #2	$198.45	10.599%	$219.4837	$219.48	$219.50	$219.50
Purchase #3	$232.32	7.765%	$250.3596	$250.36	$250.35	$250.40
Purchase #4	$122.64	13.678%	$139.4147	$139.41	$139.40	$139.40
Purchase #5	$134.51	11.613%	$150.1306	$150.13	$150.15	$150.10
Purchase #6	$15.65	9.820%	$17.1868	$17.19	$17.20	$17.20
Purchase #7	$56.60	13.618%	$64.3078	$64.31	$64.30	$64.30
7 purchase totals =	$1,000.79		$1,111.0273	$1,111.02	$1,111.05	$1,111.00