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	$213.53	13.551%	$242.4655	$242.47	$242.45	$242.50
Purchase #2	$203.80	9.218%	$222.5863	$222.59	$222.60	$222.60
Purchase #3	$181.81	5.561%	$191.9205	$191.92	$191.90	$191.90
Purchase #4	$99.65	7.301%	$106.9254	$106.93	$106.95	$106.90
Purchase #5	$126.47	7.643%	$136.1361	$136.14	$136.15	$136.10
Purchase #6	$17.55	7.731%	$18.9068	$18.91	$18.90	$18.90
Purchase #7	$107.30	11.802%	$119.9635	$119.96	$119.95	$120.00
7 purchase totals =	$950.11		$1,038.9041	$1,038.92	$1,038.90	$1,038.90