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	$119.80	3.789%	$124.3392	$124.34	$124.35	$124.30
Purchase #2	$54.95	13.582%	$62.4133	$62.41	$62.40	$62.40
Purchase #3	$52.62	9.417%	$57.5752	$57.58	$57.60	$57.60
Purchase #4	$180.52	10.132%	$198.8103	$198.81	$198.80	$198.80
Purchase #5	$136.41	9.130%	$148.8642	$148.86	$148.85	$148.90
Purchase #6	$105.41	7.301%	$113.106	$113.11	$113.10	$113.10
Purchase #7	$18.25	11.787%	$20.4011	$20.40	$20.40	$20.40
7 purchase totals =	$667.96		$725.5093	$725.51	$725.50	$725.50