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	$82.63	8.330%	$89.5131	$89.51	$89.50	$89.50
Purchase #2	$164.36	6.190%	$174.5339	$174.53	$174.55	$174.50
Purchase #3	$185.56	10.719%	$205.4502	$205.45	$205.45	$205.50
Purchase #4	$94.87	4.454%	$99.0955	$99.10	$99.10	$99.10
Purchase #5	$175.28	6.697%	$187.0185	$187.02	$187.00	$187.00
Purchase #6	$238.87	9.873%	$262.4536	$262.45	$262.45	$262.50
Purchase #7	$228.94	10.648%	$253.3175	$253.32	$253.30	$253.30
7 purchase totals =	$1,170.51		$1,271.3823	$1,271.38	$1,271.35	$1,271.40