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	$129.78	11.573%	$144.7994	$144.80	$144.80	$144.80
Purchase #2	$82.62	7.225%	$88.5893	$88.59	$88.60	$88.60
Purchase #3	$203.62	4.729%	$213.2492	$213.25	$213.25	$213.20
Purchase #4	$115.28	10.684%	$127.5965	$127.60	$127.60	$127.60
Purchase #5	$18.56	12.647%	$20.9073	$20.91	$20.90	$20.90
Purchase #6	$173.63	4.815%	$181.9903	$181.99	$182.00	$182.00
Purchase #7	$238.92	10.334%	$263.61	$263.61	$263.60	$263.60
7 purchase totals =	$962.41		$1,040.7420	$1,040.75	$1,040.75	$1,040.70