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	$104.86	12.450%	$117.9151	$117.92	$117.90	$117.90
Purchase #2	$51.30	8.774%	$55.8011	$55.80	$55.80	$55.80
Purchase #3	$79.31	13.178%	$89.7615	$89.76	$89.75	$89.80
Purchase #4	$25.30	7.600%	$27.2228	$27.22	$27.20	$27.20
Purchase #5	$232.95	10.303%	$256.9508	$256.95	$256.95	$257.00
Purchase #6	$40.88	11.649%	$45.6421	$45.64	$45.65	$45.60
Purchase #7	$82.66	6.579%	$88.0982	$88.10	$88.10	$88.10
7 purchase totals =	$617.26		$681.3916	$681.39	$681.35	$681.40