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	$25.27	7.322%	$27.1203	$27.12	$27.10	$27.10
Purchase #2	$208.51	8.274%	$225.7621	$225.76	$225.75	$225.80
Purchase #3	$176.98	10.826%	$196.1399	$196.14	$196.15	$196.10
Purchase #4	$202.78	13.689%	$230.5386	$230.54	$230.55	$230.50
Purchase #5	$98.36	5.508%	$103.7777	$103.78	$103.80	$103.80
Purchase #6	$96.94	10.261%	$106.887	$106.89	$106.90	$106.90
Purchase #7	$183.75	3.106%	$189.4573	$189.46	$189.45	$189.50
7 purchase totals =	$992.59		$1,079.6829	$1,079.69	$1,079.70	$1,079.70