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	$150.79	5.585%	$159.2116	$159.21	$159.20	$159.20
Purchase #2	$250.53	4.540%	$261.9041	$261.90	$261.90	$261.90
Purchase #3	$81.55	10.782%	$90.3427	$90.34	$90.35	$90.30
Purchase #4	$48.70	3.851%	$50.5754	$50.58	$50.60	$50.60
Purchase #5	$169.61	10.579%	$187.553	$187.55	$187.55	$187.60
Purchase #6	$161.58	11.244%	$179.7481	$179.75	$179.75	$179.70
Purchase #7	$114.57	7.384%	$123.0298	$123.03	$123.05	$123.00
7 purchase totals =	$977.33		$1,052.3647	$1,052.36	$1,052.40	$1,052.30