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	$24.79	10.751%	$27.4552	$27.46	$27.45	$27.50
Purchase #2	$179.79	9.134%	$196.212	$196.21	$196.20	$196.20
Purchase #3	$33.29	12.662%	$37.5052	$37.51	$37.50	$37.50
Purchase #4	$38.98	10.814%	$43.1953	$43.20	$43.20	$43.20
Purchase #5	$16.74	13.257%	$18.9592	$18.96	$18.95	$19.00
Purchase #6	$32.87	5.433%	$34.6558	$34.66	$34.65	$34.70
Purchase #7	$74.92	4.850%	$78.5536	$78.55	$78.55	$78.60
7 purchase totals =	$401.38		$436.5363	$436.55	$436.50	$436.70