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	$49.32	12.499%	$55.4845	$55.48	$55.50	$55.50
Purchase #2	$19.88	10.231%	$21.9139	$21.91	$21.90	$21.90
Purchase #3	$63.99	5.739%	$67.6624	$67.66	$67.65	$67.70
Purchase #4	$47.82	8.479%	$51.8747	$51.87	$51.85	$51.90
Purchase #5	$77.52	10.268%	$85.4798	$85.48	$85.50	$85.50
Purchase #6	$165.94	8.197%	$179.5421	$179.54	$179.55	$179.50
Purchase #7	$57.32	6.869%	$61.2573	$61.26	$61.25	$61.30
7 purchase totals =	$481.79		$523.2147	$523.20	$523.20	$523.30