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	$73.36	6.533%	$78.1526	$78.15	$78.15	$78.20
Purchase #2	$194.25	11.473%	$216.5363	$216.54	$216.55	$216.50
Purchase #3	$155.89	8.798%	$169.6052	$169.61	$169.60	$169.60
Purchase #4	$171.34	7.225%	$183.7193	$183.72	$183.70	$183.70
Purchase #5	$101.60	10.770%	$112.5423	$112.54	$112.55	$112.50
Purchase #6	$63.57	12.874%	$71.754	$71.75	$71.75	$71.80
Purchase #7	$115.31	4.135%	$120.0781	$120.08	$120.10	$120.10
7 purchase totals =	$875.32		$952.3878	$952.39	$952.40	$952.40