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	$5.78	8.167%	$6.2521	$6.25	$6.25	$6.30
Purchase #2	$120.44	10.735%	$133.3692	$133.37	$133.35	$133.40
Purchase #3	$135.40	5.139%	$142.3582	$142.36	$142.35	$142.40
Purchase #4	$83.28	7.553%	$89.5701	$89.57	$89.55	$89.60
Purchase #5	$99.74	11.480%	$111.1902	$111.19	$111.20	$111.20
Purchase #6	$76.99	11.588%	$85.9116	$85.91	$85.90	$85.90
Purchase #7	$223.84	12.402%	$251.6006	$251.60	$251.60	$251.60
7 purchase totals =	$745.47		$820.2520	$820.25	$820.20	$820.40