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	$166.71	11.775%	$186.3401	$186.34	$186.35	$186.30
Purchase #2	$233.86	6.642%	$249.393	$249.39	$249.40	$249.40
Purchase #3	$79.29	13.178%	$89.7388	$89.74	$89.75	$89.70
Purchase #4	$241.44	10.385%	$266.5135	$266.51	$266.50	$266.50
Purchase #5	$44.62	13.868%	$50.8079	$50.81	$50.80	$50.80
Purchase #6	$164.96	4.471%	$172.3354	$172.34	$172.35	$172.30
Purchase #7	$99.39	4.780%	$104.1408	$104.14	$104.15	$104.10
7 purchase totals =	$1,030.27		$1,119.2695	$1,119.27	$1,119.30	$1,119.10