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	$168.56	3.127%	$173.8309	$173.83	$173.85	$173.80
Purchase #2	$55.75	4.216%	$58.1004	$58.10	$58.10	$58.10
Purchase #3	$132.27	5.752%	$139.8782	$139.88	$139.90	$139.90
Purchase #4	$83.98	10.190%	$92.5376	$92.54	$92.55	$92.50
Purchase #5	$95.85	11.651%	$107.0175	$107.02	$107.00	$107.00
Purchase #6	$192.98	13.197%	$218.4476	$218.45	$218.45	$218.40
Purchase #7	$80.26	11.754%	$89.6938	$89.69	$89.70	$89.70
7 purchase totals =	$809.65		$879.5060	$879.51	$879.55	$879.40