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	$38.87	12.375%	$43.6802	$43.68	$43.70	$43.70
Purchase #2	$16.63	11.289%	$18.5074	$18.51	$18.50	$18.50
Purchase #3	$56.31	5.497%	$59.4054	$59.41	$59.40	$59.40
Purchase #4	$241.37	6.615%	$257.3366	$257.34	$257.35	$257.30
Purchase #5	$56.85	4.397%	$59.3497	$59.35	$59.35	$59.30
Purchase #6	$182.56	4.862%	$191.4361	$191.44	$191.45	$191.40
Purchase #7	$186.63	13.214%	$211.2913	$211.29	$211.30	$211.30
7 purchase totals =	$779.22		$841.0067	$841.02	$841.05	$840.90