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	$111.79	10.306%	$123.3111	$123.31	$123.30	$123.30
Purchase #2	$78.30	3.329%	$80.9066	$80.91	$80.90	$80.90
Purchase #3	$46.28	12.306%	$51.9752	$51.98	$52.00	$52.00
Purchase #4	$206.46	5.122%	$217.0349	$217.03	$217.05	$217.00
Purchase #5	$196.69	7.450%	$211.3434	$211.34	$211.35	$211.30
Purchase #6	$79.36	4.666%	$83.0629	$83.06	$83.05	$83.10
Purchase #7	$18.68	8.707%	$20.3065	$20.31	$20.30	$20.30
7 purchase totals =	$737.56		$787.9406	$787.94	$787.95	$787.90