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	$62.41	5.238%	$65.679	$65.68	$65.70	$65.70
Purchase #2	$96.33	5.566%	$101.6917	$101.69	$101.70	$101.70
Purchase #3	$240.53	12.659%	$270.9787	$270.98	$271.00	$271.00
Purchase #4	$210.39	13.171%	$238.1005	$238.10	$238.10	$238.10
Purchase #5	$72.34	13.222%	$81.9048	$81.90	$81.90	$81.90
Purchase #6	$200.74	4.838%	$210.4518	$210.45	$210.45	$210.50
Purchase #7	$9.58	4.826%	$10.0423	$10.04	$10.05	$10.00
7 purchase totals =	$892.32		$978.8488	$978.84	$978.90	$978.90