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	$62.66	12.113%	$70.25	$70.25	$70.25	$70.30
Purchase #2	$35.91	12.786%	$40.5015	$40.50	$40.50	$40.50
Purchase #3	$195.39	13.653%	$222.0666	$222.07	$222.05	$222.10
Purchase #4	$108.47	13.230%	$122.8206	$122.82	$122.80	$122.80
Purchase #5	$18.62	4.637%	$19.4834	$19.48	$19.50	$19.50
Purchase #6	$142.47	5.815%	$150.7546	$150.75	$150.75	$150.80
Purchase #7	$171.78	8.473%	$186.3349	$186.33	$186.35	$186.30
7 purchase totals =	$735.30		$812.2116	$812.20	$812.20	$812.30