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	$156.42	9.495%	$171.2721	$171.27	$171.25	$171.30
Purchase #2	$133.84	12.728%	$150.8752	$150.88	$150.90	$150.90
Purchase #3	$22.64	7.640%	$24.3697	$24.37	$24.35	$24.40
Purchase #4	$162.58	10.862%	$180.2394	$180.24	$180.25	$180.20
Purchase #5	$34.49	8.414%	$37.392	$37.39	$37.40	$37.40
Purchase #6	$123.77	10.619%	$136.9131	$136.91	$136.90	$136.90
Purchase #7	$65.57	9.499%	$71.7985	$71.80	$71.80	$71.80
7 purchase totals =	$699.31		$772.8600	$772.86	$772.85	$772.90