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	$232.91	13.555%	$264.481	$264.48	$264.50	$264.50
Purchase #2	$24.41	3.714%	$25.3166	$25.32	$25.30	$25.30
Purchase #3	$113.44	11.316%	$126.2769	$126.28	$126.30	$126.30
Purchase #4	$46.54	11.448%	$51.8679	$51.87	$51.85	$51.90
Purchase #5	$114.86	3.586%	$118.9789	$118.98	$119.00	$119.00
Purchase #6	$85.93	3.737%	$89.1412	$89.14	$89.15	$89.10
Purchase #7	$133.72	7.607%	$143.8921	$143.89	$143.90	$143.90
7 purchase totals =	$751.81		$819.9546	$819.96	$820.00	$820.00