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	$151.46	13.689%	$172.1934	$172.19	$172.20	$172.20
Purchase #2	$50.60	5.119%	$53.1902	$53.19	$53.20	$53.20
Purchase #3	$189.46	9.577%	$207.6046	$207.60	$207.60	$207.60
Purchase #4	$212.80	12.236%	$238.8382	$238.84	$238.85	$238.80
Purchase #5	$82.29	9.157%	$89.8253	$89.83	$89.85	$89.80
Purchase #6	$9.40	11.279%	$10.4602	$10.46	$10.45	$10.50
Purchase #7	$187.90	11.250%	$209.0388	$209.04	$209.05	$209.00
7 purchase totals =	$883.91		$981.1507	$981.15	$981.20	$981.10