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	$52.86	4.714%	$55.3518	$55.35	$55.35	$55.40
Purchase #2	$210.80	11.839%	$235.7566	$235.76	$235.75	$235.80
Purchase #3	$21.67	3.574%	$22.4445	$22.44	$22.45	$22.40
Purchase #4	$24.32	13.774%	$27.6698	$27.67	$27.65	$27.70
Purchase #5	$172.83	8.698%	$187.8628	$187.86	$187.85	$187.90
Purchase #6	$46.89	13.742%	$53.3336	$53.33	$53.35	$53.30
Purchase #7	$37.36	8.192%	$40.4205	$40.42	$40.40	$40.40
7 purchase totals =	$566.73		$622.8396	$622.83	$622.80	$622.90