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	$134.40	12.780%	$151.5763	$151.58	$151.60	$151.60
Purchase #2	$192.78	7.831%	$207.8766	$207.88	$207.90	$207.90
Purchase #3	$240.42	7.771%	$259.103	$259.10	$259.10	$259.10
Purchase #4	$22.37	9.618%	$24.5215	$24.52	$24.50	$24.50
Purchase #5	$54.98	11.459%	$61.2802	$61.28	$61.30	$61.30
Purchase #6	$166.35	3.310%	$171.8562	$171.86	$171.85	$171.90
Purchase #7	$193.56	5.552%	$204.3065	$204.31	$204.30	$204.30
7 purchase totals =	$1,004.86		$1,080.5203	$1,080.53	$1,080.55	$1,080.60