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	$25.98	4.354%	$27.1112	$27.11	$27.10	$27.10
Purchase #2	$80.96	12.870%	$91.3796	$91.38	$91.40	$91.40
Purchase #3	$109.47	11.261%	$121.7974	$121.80	$121.80	$121.80
Purchase #4	$215.90	8.156%	$233.5088	$233.51	$233.50	$233.50
Purchase #5	$151.31	8.622%	$164.3559	$164.36	$164.35	$164.40
Purchase #6	$243.92	10.603%	$269.7828	$269.78	$269.80	$269.80
Purchase #7	$104.85	9.322%	$114.6241	$114.62	$114.60	$114.60
7 purchase totals =	$932.39		$1,022.5598	$1,022.56	$1,022.55	$1,022.60