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	$86.45	4.132%	$90.0221	$90.02	$90.00	$90.00
Purchase #2	$116.98	10.418%	$129.167	$129.17	$129.15	$129.20
Purchase #3	$221.43	9.483%	$242.4282	$242.43	$242.45	$242.40
Purchase #4	$161.87	12.571%	$182.2187	$182.22	$182.20	$182.20
Purchase #5	$21.91	10.231%	$24.1516	$24.15	$24.15	$24.20
Purchase #6	$227.29	12.341%	$255.3399	$255.34	$255.35	$255.30
Purchase #7	$119.30	6.747%	$127.3492	$127.35	$127.35	$127.30
7 purchase totals =	$955.23		$1,050.6767	$1,050.68	$1,050.65	$1,050.60