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	$250.50	11.427%	$279.1246	$279.12	$279.10	$279.10
Purchase #2	$179.49	9.389%	$196.3423	$196.34	$196.35	$196.30
Purchase #3	$85.27	5.407%	$89.8805	$89.88	$89.90	$89.90
Purchase #4	$241.98	8.700%	$263.0323	$263.03	$263.05	$263.00
Purchase #5	$235.35	5.604%	$248.539	$248.54	$248.55	$248.50
Purchase #6	$46.85	5.652%	$49.498	$49.50	$49.50	$49.50
Purchase #7	$134.28	3.597%	$139.1101	$139.11	$139.10	$139.10
7 purchase totals =	$1,173.72		$1,265.5268	$1,265.52	$1,265.55	$1,265.40