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	$72.61	8.697%	$78.9249	$78.92	$78.90	$78.90
Purchase #2	$225.44	11.482%	$251.325	$251.33	$251.35	$251.30
Purchase #3	$51.47	9.282%	$56.2474	$56.25	$56.25	$56.20
Purchase #4	$92.62	11.606%	$103.3695	$103.37	$103.35	$103.40
Purchase #5	$230.42	5.801%	$243.7867	$243.79	$243.80	$243.80
Purchase #6	$159.59	7.528%	$171.6039	$171.60	$171.60	$171.60
Purchase #7	$74.72	9.497%	$81.8162	$81.82	$81.80	$81.80
7 purchase totals =	$906.87		$987.0736	$987.08	$987.05	$987.00