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	$151.33	5.314%	$159.3717	$159.37	$159.35	$159.40
Purchase #2	$73.53	5.504%	$77.5771	$77.58	$77.60	$77.60
Purchase #3	$98.52	11.372%	$109.7237	$109.72	$109.70	$109.70
Purchase #4	$169.46	10.378%	$187.0466	$187.05	$187.05	$187.00
Purchase #5	$138.54	5.766%	$146.5282	$146.53	$146.55	$146.50
Purchase #6	$199.89	4.841%	$209.5667	$209.57	$209.55	$209.60
Purchase #7	$177.79	12.710%	$200.3871	$200.39	$200.40	$200.40
7 purchase totals =	$1,009.06		$1,090.2011	$1,090.21	$1,090.20	$1,090.20