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	$98.84	11.131%	$109.8419	$109.84	$109.85	$109.80
Purchase #2	$90.41	8.771%	$98.3399	$98.34	$98.35	$98.30
Purchase #3	$170.31	13.256%	$192.8863	$192.89	$192.90	$192.90
Purchase #4	$165.32	4.615%	$172.9495	$172.95	$172.95	$172.90
Purchase #5	$75.68	5.445%	$79.8008	$79.80	$79.80	$79.80
Purchase #6	$81.25	10.421%	$89.7171	$89.72	$89.70	$89.70
Purchase #7	$36.74	4.324%	$38.3286	$38.33	$38.35	$38.30
7 purchase totals =	$718.55		$781.8641	$781.87	$781.90	$781.70