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	$107.99	10.605%	$119.4423	$119.44	$119.45	$119.40
Purchase #2	$90.45	4.681%	$94.684	$94.68	$94.70	$94.70
Purchase #3	$11.69	5.266%	$12.3056	$12.31	$12.30	$12.30
Purchase #4	$77.36	8.412%	$83.8675	$83.87	$83.85	$83.90
Purchase #5	$229.80	12.352%	$258.1849	$258.18	$258.20	$258.20
Purchase #6	$65.26	3.460%	$67.518	$67.52	$67.50	$67.50
Purchase #7	$97.59	12.173%	$109.4696	$109.47	$109.45	$109.50
7 purchase totals =	$680.14		$745.4719	$745.47	$745.45	$745.50