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	$133.81	13.411%	$151.7553	$151.76	$151.75	$151.80
Purchase #2	$115.78	13.109%	$130.9576	$130.96	$130.95	$131.00
Purchase #3	$78.97	13.695%	$89.7849	$89.78	$89.80	$89.80
Purchase #4	$248.57	13.110%	$281.1575	$281.16	$281.15	$281.20
Purchase #5	$73.66	9.736%	$80.8315	$80.83	$80.85	$80.80
Purchase #6	$144.65	11.611%	$161.4453	$161.45	$161.45	$161.40
Purchase #7	$5.69	4.771%	$5.9615	$5.96	$5.95	$6.00
7 purchase totals =	$801.13		$901.8936	$901.90	$901.90	$902.00