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	$186.42	3.431%	$192.8161	$192.82	$192.80	$192.80
Purchase #2	$153.67	11.620%	$171.5265	$171.53	$171.55	$171.50
Purchase #3	$248.37	12.839%	$280.2582	$280.26	$280.25	$280.30
Purchase #4	$178.71	3.630%	$185.1972	$185.20	$185.20	$185.20
Purchase #5	$56.68	4.567%	$59.2686	$59.27	$59.25	$59.30
Purchase #6	$92.59	12.399%	$104.0702	$104.07	$104.05	$104.10
Purchase #7	$67.35	7.544%	$72.4309	$72.43	$72.45	$72.40
7 purchase totals =	$983.79		$1,065.5677	$1,065.58	$1,065.55	$1,065.60