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	$151.54	11.192%	$168.5004	$168.50	$168.50	$168.50
Purchase #2	$190.55	10.543%	$210.6397	$210.64	$210.65	$210.60
Purchase #3	$116.46	12.675%	$131.2213	$131.22	$131.20	$131.20
Purchase #4	$21.59	10.862%	$23.9351	$23.94	$23.95	$23.90
Purchase #5	$216.74	11.638%	$241.9642	$241.96	$241.95	$242.00
Purchase #6	$152.92	11.184%	$170.0226	$170.02	$170.00	$170.00
Purchase #7	$241.86	3.296%	$249.8317	$249.83	$249.85	$249.80
7 purchase totals =	$1,091.66		$1,196.1150	$1,196.11	$1,196.10	$1,196.00