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	$226.81	7.102%	$242.918	$242.92	$242.90	$242.90
Purchase #2	$233.60	6.584%	$248.9802	$248.98	$249.00	$249.00
Purchase #3	$36.89	5.783%	$39.0233	$39.02	$39.00	$39.00
Purchase #4	$76.42	7.465%	$82.1248	$82.12	$82.10	$82.10
Purchase #5	$36.72	12.421%	$41.281	$41.28	$41.30	$41.30
Purchase #6	$51.27	9.540%	$56.1612	$56.16	$56.15	$56.20
Purchase #7	$175.57	3.326%	$181.4095	$181.41	$181.40	$181.40
7 purchase totals =	$837.28		$891.8980	$891.89	$891.85	$891.90