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	$124.66	5.209%	$131.1535	$131.15	$131.15	$131.20
Purchase #2	$173.50	9.265%	$189.5748	$189.57	$189.55	$189.60
Purchase #3	$136.92	11.639%	$152.8561	$152.86	$152.85	$152.90
Purchase #4	$102.45	13.462%	$116.2418	$116.24	$116.25	$116.20
Purchase #5	$123.62	4.371%	$129.0234	$129.02	$129.00	$129.00
Purchase #6	$143.80	5.757%	$152.0786	$152.08	$152.10	$152.10
Purchase #7	$56.32	5.134%	$59.2115	$59.21	$59.20	$59.20
7 purchase totals =	$861.27		$930.1397	$930.13	$930.10	$930.20