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	$153.68	12.183%	$172.4028	$172.40	$172.40	$172.40
Purchase #2	$171.40	8.844%	$186.5586	$186.56	$186.55	$186.60
Purchase #3	$241.70	13.161%	$273.5101	$273.51	$273.50	$273.50
Purchase #4	$5.43	13.395%	$6.1573	$6.16	$6.15	$6.20
Purchase #5	$48.82	9.231%	$53.3266	$53.33	$53.35	$53.30
Purchase #6	$105.91	8.528%	$114.942	$114.94	$114.95	$114.90
Purchase #7	$210.55	10.872%	$233.441	$233.44	$233.45	$233.40
7 purchase totals =	$937.49		$1,040.3384	$1,040.34	$1,040.35	$1,040.30