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	$92.56	7.736%	$99.7204	$99.72	$99.70	$99.70
Purchase #2	$182.25	6.199%	$193.5477	$193.55	$193.55	$193.50
Purchase #3	$124.56	9.223%	$136.0482	$136.05	$136.05	$136.00
Purchase #4	$53.71	4.530%	$56.1431	$56.14	$56.15	$56.10
Purchase #5	$74.81	11.569%	$83.4648	$83.46	$83.45	$83.50
Purchase #6	$62.47	4.553%	$65.3143	$65.31	$65.30	$65.30
Purchase #7	$13.79	9.709%	$15.1289	$15.13	$15.15	$15.10
7 purchase totals =	$604.15		$649.3674	$649.36	$649.35	$649.20