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	$64.88	8.555%	$70.4305	$70.43	$70.45	$70.40
Purchase #2	$198.31	10.867%	$219.8603	$219.86	$219.85	$219.90
Purchase #3	$210.28	6.534%	$224.0197	$224.02	$224.00	$224.00
Purchase #4	$18.90	10.869%	$20.9542	$20.95	$20.95	$21.00
Purchase #5	$175.93	5.219%	$185.1118	$185.11	$185.10	$185.10
Purchase #6	$215.35	10.647%	$238.2783	$238.28	$238.30	$238.30
Purchase #7	$117.33	9.669%	$128.6746	$128.67	$128.65	$128.70
7 purchase totals =	$1,000.98		$1,087.3294	$1,087.32	$1,087.30	$1,087.40