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	$21.50	7.490%	$23.1104	$23.11	$23.10	$23.10
Purchase #2	$43.79	3.175%	$45.1803	$45.18	$45.20	$45.20
Purchase #3	$60.50	10.456%	$66.8259	$66.83	$66.85	$66.80
Purchase #4	$192.56	8.615%	$209.149	$209.15	$209.15	$209.10
Purchase #5	$33.42	11.797%	$37.3626	$37.36	$37.35	$37.40
Purchase #6	$14.60	9.241%	$15.9492	$15.95	$15.95	$15.90
Purchase #7	$18.60	7.437%	$19.9833	$19.98	$20.00	$20.00
7 purchase totals =	$384.97		$417.5607	$417.56	$417.60	$417.50