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	$134.57	5.857%	$142.4518	$142.45	$142.45	$142.50
Purchase #2	$103.82	10.736%	$114.9661	$114.97	$114.95	$115.00
Purchase #3	$152.77	4.396%	$159.4858	$159.49	$159.50	$159.50
Purchase #4	$86.29	5.245%	$90.8159	$90.82	$90.80	$90.80
Purchase #5	$67.36	3.835%	$69.9433	$69.94	$69.95	$69.90
Purchase #6	$79.70	13.603%	$90.5416	$90.54	$90.55	$90.50
Purchase #7	$250.56	7.636%	$269.6928	$269.69	$269.70	$269.70
7 purchase totals =	$875.07		$937.8973	$937.90	$937.90	$937.90