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	$239.32	4.279%	$249.5605	$249.56	$249.55	$249.60
Purchase #2	$167.96	8.144%	$181.6387	$181.64	$181.65	$181.60
Purchase #3	$183.29	7.828%	$197.6379	$197.64	$197.65	$197.60
Purchase #4	$41.54	10.146%	$45.7546	$45.75	$45.75	$45.80
Purchase #5	$72.52	11.575%	$80.9142	$80.91	$80.90	$80.90
Purchase #6	$241.33	6.206%	$256.3069	$256.31	$256.30	$256.30
Purchase #7	$55.69	6.281%	$59.1879	$59.19	$59.20	$59.20
7 purchase totals =	$1,001.65		$1,071.0007	$1,071.00	$1,071.00	$1,071.00