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	$42.33	12.536%	$47.6365	$47.64	$47.65	$47.60
Purchase #2	$100.59	12.765%	$113.4303	$113.43	$113.45	$113.40
Purchase #3	$30.88	3.843%	$32.0667	$32.07	$32.05	$32.10
Purchase #4	$155.46	11.599%	$173.4918	$173.49	$173.50	$173.50
Purchase #5	$34.88	10.582%	$38.571	$38.57	$38.55	$38.60
Purchase #6	$235.48	3.507%	$243.7383	$243.74	$243.75	$243.70
Purchase #7	$156.77	9.483%	$171.6365	$171.64	$171.65	$171.60
7 purchase totals =	$756.39		$820.5711	$820.58	$820.60	$820.50