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	$110.32	11.658%	$123.1811	$123.18	$123.20	$123.20
Purchase #2	$38.28	12.531%	$43.0769	$43.08	$43.10	$43.10
Purchase #3	$9.50	8.310%	$10.2895	$10.29	$10.30	$10.30
Purchase #4	$90.38	8.816%	$98.3479	$98.35	$98.35	$98.30
Purchase #5	$145.55	4.682%	$152.3647	$152.36	$152.35	$152.40
Purchase #6	$135.61	9.170%	$148.0454	$148.05	$148.05	$148.00
Purchase #7	$67.59	10.785%	$74.8796	$74.88	$74.90	$74.90
7 purchase totals =	$597.23		$650.1851	$650.19	$650.25	$650.20