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	$248.77	3.389%	$257.2008	$257.20	$257.20	$257.20
Purchase #2	$170.51	8.214%	$184.5157	$184.52	$184.50	$184.50
Purchase #3	$160.74	9.298%	$175.6856	$175.69	$175.70	$175.70
Purchase #4	$206.83	4.216%	$215.55	$215.55	$215.55	$215.60
Purchase #5	$45.63	13.492%	$51.7864	$51.79	$51.80	$51.80
Purchase #6	$59.52	13.772%	$67.7171	$67.72	$67.70	$67.70
Purchase #7	$173.46	3.366%	$179.2987	$179.30	$179.30	$179.30
7 purchase totals =	$1,065.46		$1,131.7543	$1,131.77	$1,131.75	$1,131.80