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	$122.27	4.426%	$127.6817	$127.68	$127.70	$127.70
Purchase #2	$65.61	11.174%	$72.9413	$72.94	$72.95	$72.90
Purchase #3	$95.33	7.400%	$102.3844	$102.38	$102.40	$102.40
Purchase #4	$165.71	10.375%	$182.9024	$182.90	$182.90	$182.90
Purchase #5	$143.96	7.720%	$155.0737	$155.07	$155.05	$155.10
Purchase #6	$36.94	11.582%	$41.2184	$41.22	$41.20	$41.20
Purchase #7	$134.33	13.667%	$152.6889	$152.69	$152.70	$152.70
7 purchase totals =	$764.15		$834.8908	$834.88	$834.90	$834.90