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	$73.44	7.373%	$78.8547	$78.85	$78.85	$78.90
Purchase #2	$75.48	7.380%	$81.0504	$81.05	$81.05	$81.10
Purchase #3	$203.44	6.131%	$215.9129	$215.91	$215.90	$215.90
Purchase #4	$237.37	13.642%	$269.752	$269.75	$269.75	$269.80
Purchase #5	$28.40	10.772%	$31.4592	$31.46	$31.45	$31.50
Purchase #6	$174.88	9.405%	$191.3275	$191.33	$191.35	$191.30
Purchase #7	$62.92	3.826%	$65.3273	$65.33	$65.35	$65.30
7 purchase totals =	$855.93		$933.6840	$933.68	$933.70	$933.80