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	$120.80	12.815%	$136.2805	$136.28	$136.30	$136.30
Purchase #2	$236.75	5.108%	$248.8432	$248.84	$248.85	$248.80
Purchase #3	$98.77	12.449%	$111.0659	$111.07	$111.05	$111.10
Purchase #4	$123.78	8.157%	$133.8767	$133.88	$133.90	$133.90
Purchase #5	$100.93	13.702%	$114.7594	$114.76	$114.75	$114.80
Purchase #6	$82.75	9.389%	$90.5194	$90.52	$90.50	$90.50
Purchase #7	$136.69	10.477%	$151.011	$151.01	$151.00	$151.00
7 purchase totals =	$900.47		$986.3561	$986.36	$986.35	$986.40