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	$95.27	12.539%	$107.2159	$107.22	$107.20	$107.20
Purchase #2	$226.69	12.159%	$254.2532	$254.25	$254.25	$254.30
Purchase #3	$75.92	13.177%	$85.924	$85.92	$85.90	$85.90
Purchase #4	$182.62	4.734%	$191.2652	$191.27	$191.25	$191.30
Purchase #5	$43.38	3.723%	$44.995	$45.00	$45.00	$45.00
Purchase #6	$151.54	9.309%	$165.6469	$165.65	$165.65	$165.60
Purchase #7	$108.56	13.406%	$123.1136	$123.11	$123.10	$123.10
7 purchase totals =	$883.98		$972.4138	$972.42	$972.35	$972.40