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	$83.98	9.624%	$92.0622	$92.06	$92.05	$92.10
Purchase #2	$114.98	7.682%	$123.8128	$123.81	$123.80	$123.80
Purchase #3	$229.72	11.157%	$255.3499	$255.35	$255.35	$255.30
Purchase #4	$31.34	11.139%	$34.831	$34.83	$34.85	$34.80
Purchase #5	$110.74	5.787%	$117.1485	$117.15	$117.15	$117.10
Purchase #6	$65.50	12.161%	$73.4655	$73.47	$73.45	$73.50
Purchase #7	$197.46	12.325%	$221.7969	$221.80	$221.80	$221.80
7 purchase totals =	$833.72		$918.4668	$918.47	$918.45	$918.40