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	$41.80	5.306%	$44.0179	$44.02	$44.00	$44.00
Purchase #2	$250.35	13.150%	$283.271	$283.27	$283.25	$283.30
Purchase #3	$75.56	13.409%	$85.6918	$85.69	$85.70	$85.70
Purchase #4	$81.66	5.159%	$85.8728	$85.87	$85.85	$85.90
Purchase #5	$50.90	6.327%	$54.1204	$54.12	$54.10	$54.10
Purchase #6	$127.50	9.288%	$139.3422	$139.34	$139.35	$139.30
Purchase #7	$40.78	3.171%	$42.0731	$42.07	$42.05	$42.10
7 purchase totals =	$668.55		$734.3892	$734.38	$734.30	$734.40