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	$167.60	11.457%	$186.8019	$186.80	$186.80	$186.80
Purchase #2	$44.82	12.845%	$50.5771	$50.58	$50.60	$50.60
Purchase #3	$26.72	7.102%	$28.6177	$28.62	$28.60	$28.60
Purchase #4	$82.38	9.593%	$90.2827	$90.28	$90.30	$90.30
Purchase #5	$115.51	9.826%	$126.86	$126.86	$126.85	$126.90
Purchase #6	$130.46	13.338%	$147.8608	$147.86	$147.85	$147.90
Purchase #7	$62.62	9.841%	$68.7824	$68.78	$68.80	$68.80
7 purchase totals =	$630.11		$699.7826	$699.78	$699.80	$699.90