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	$95.36	5.455%	$100.5619	$100.56	$100.55	$100.60
Purchase #2	$161.61	3.859%	$167.8465	$167.85	$167.85	$167.80
Purchase #3	$94.84	11.661%	$105.8993	$105.90	$105.90	$105.90
Purchase #4	$200.35	4.391%	$209.1474	$209.15	$209.15	$209.10
Purchase #5	$162.38	9.690%	$178.1146	$178.11	$178.10	$178.10
Purchase #6	$187.32	3.836%	$194.5056	$194.51	$194.50	$194.50
Purchase #7	$163.55	10.112%	$180.0882	$180.09	$180.10	$180.10
7 purchase totals =	$1,065.41		$1,136.1635	$1,136.17	$1,136.15	$1,136.10