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	$52.35	6.817%	$55.9187	$55.92	$55.90	$55.90
Purchase #2	$178.52	7.306%	$191.5627	$191.56	$191.55	$191.60
Purchase #3	$133.30	7.840%	$143.7507	$143.75	$143.75	$143.80
Purchase #4	$127.61	9.243%	$139.405	$139.41	$139.40	$139.40
Purchase #5	$94.78	13.648%	$107.7156	$107.72	$107.70	$107.70
Purchase #6	$150.80	7.463%	$162.0542	$162.05	$162.05	$162.10
Purchase #7	$165.55	12.282%	$185.8829	$185.88	$185.90	$185.90
7 purchase totals =	$902.91		$986.2898	$986.29	$986.25	$986.40