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	$133.80	3.386%	$138.3305	$138.33	$138.35	$138.30
Purchase #2	$28.97	10.850%	$32.1132	$32.11	$32.10	$32.10
Purchase #3	$25.80	7.842%	$27.8232	$27.82	$27.80	$27.80
Purchase #4	$202.78	9.527%	$222.0989	$222.10	$222.10	$222.10
Purchase #5	$130.32	6.784%	$139.1609	$139.16	$139.15	$139.20
Purchase #6	$98.87	11.144%	$109.8881	$109.89	$109.90	$109.90
Purchase #7	$135.53	10.292%	$149.4787	$149.48	$149.50	$149.50
7 purchase totals =	$756.07		$818.8935	$818.89	$818.90	$818.90