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	$89.87	7.289%	$96.4206	$96.42	$96.40	$96.40
Purchase #2	$51.78	7.693%	$55.7634	$55.76	$55.75	$55.80
Purchase #3	$126.46	6.357%	$134.4991	$134.50	$134.50	$134.50
Purchase #4	$243.71	11.410%	$271.5173	$271.52	$271.50	$271.50
Purchase #5	$103.81	4.592%	$108.577	$108.58	$108.60	$108.60
Purchase #6	$134.65	8.294%	$145.8179	$145.82	$145.80	$145.80
Purchase #7	$167.70	13.621%	$190.5424	$190.54	$190.55	$190.50
7 purchase totals =	$917.98		$1,003.1377	$1,003.14	$1,003.10	$1,003.10