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	$126.93	13.673%	$144.2851	$144.29	$144.30	$144.30
Purchase #2	$116.60	6.300%	$123.9458	$123.95	$123.95	$123.90
Purchase #3	$75.97	12.320%	$85.3295	$85.33	$85.35	$85.30
Purchase #4	$80.67	10.612%	$89.2307	$89.23	$89.25	$89.20
Purchase #5	$117.59	3.466%	$121.6657	$121.67	$121.65	$121.70
Purchase #6	$218.74	12.143%	$245.3016	$245.30	$245.30	$245.30
Purchase #7	$242.59	9.417%	$265.4347	$265.43	$265.45	$265.40
7 purchase totals =	$979.09		$1,075.1931	$1,075.20	$1,075.25	$1,075.10