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	$122.25	12.315%	$137.3051	$137.31	$137.30	$137.30
Purchase #2	$52.93	4.421%	$55.27	$55.27	$55.25	$55.30
Purchase #3	$247.97	12.222%	$278.2769	$278.28	$278.30	$278.30
Purchase #4	$105.72	10.826%	$117.1652	$117.17	$117.15	$117.20
Purchase #5	$250.91	12.670%	$282.7003	$282.70	$282.70	$282.70
Purchase #6	$176.70	11.271%	$196.6159	$196.62	$196.60	$196.60
Purchase #7	$240.82	12.735%	$271.4884	$271.49	$271.50	$271.50
7 purchase totals =	$1,197.30		$1,338.8218	$1,338.84	$1,338.80	$1,338.90