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	$94.97	8.591%	$103.1289	$103.13	$103.15	$103.10
Purchase #2	$157.57	5.565%	$166.3388	$166.34	$166.35	$166.30
Purchase #3	$226.69	7.135%	$242.8643	$242.86	$242.85	$242.90
Purchase #4	$137.39	9.811%	$150.8693	$150.87	$150.85	$150.90
Purchase #5	$28.93	8.695%	$31.4455	$31.45	$31.45	$31.40
Purchase #6	$50.45	9.798%	$55.3931	$55.39	$55.40	$55.40
Purchase #7	$44.59	3.673%	$46.2278	$46.23	$46.25	$46.20
7 purchase totals =	$740.59		$796.2677	$796.27	$796.30	$796.20